diff --git a/bellman/src/domain.rs b/bellman/src/domain.rs
index c636855..ddba4f4 100644
--- a/bellman/src/domain.rs
+++ b/bellman/src/domain.rs
@@ -1,14 +1,15 @@
-//! This module contains an `EvaluationDomain` abstraction for
-//! performing various kinds of polynomial arithmetic on top of
-//! the scalar field.
+//! This module contains an [`EvaluationDomain`] abstraction for performing
+//! various kinds of polynomial arithmetic on top of the scalar field.
 //!
-//! In pairing-based SNARKs like Groth16, we need to calculate
-//! a quotient polynomial over a target polynomial with roots
-//! at distinct points associated with each constraint of the
-//! constraint system. In order to be efficient, we choose these
-//! roots to be the powers of a 2^n root of unity in the field.
-//! This allows us to perform polynomial operations in O(n)
-//! by performing an O(n log n) FFT over such a domain.
+//! In pairing-based SNARKs like [Groth16], we need to calculate a quotient
+//! polynomial over a target polynomial with roots at distinct points associated
+//! with each constraint of the constraint system. In order to be efficient, we
+//! choose these roots to be the powers of a 2<sup>n</sup> root of unity in the
+//! field. This allows us to perform polynomial operations in O(n) by performing
+//! an O(n log n) FFT over such a domain.
+//!
+//! [`EvaluationDomain`]: crate::domain::EvaluationDomain
+//! [Groth16]: https://eprint.iacr.org/2016/260
 
 use ff::{Field, PrimeField, ScalarEngine};
 use group::CurveProjective;
diff --git a/bellman/src/gadgets.rs b/bellman/src/gadgets.rs
index cf366df..b0ce734 100644
--- a/bellman/src/gadgets.rs
+++ b/bellman/src/gadgets.rs
@@ -1,3 +1,5 @@
+//! Self-contained sub-circuit implementations for various primitives.
+
 pub mod test;
 
 pub mod blake2s;
diff --git a/bellman/src/gadgets/blake2s.rs b/bellman/src/gadgets/blake2s.rs
index 96e554b..e98fd55 100644
--- a/bellman/src/gadgets/blake2s.rs
+++ b/bellman/src/gadgets/blake2s.rs
@@ -1,3 +1,7 @@
+//! The [BLAKE2s] hash function with personalization support.
+//!
+//! [BLAKE2s]: https://tools.ietf.org/html/rfc7693
+
 use super::{boolean::Boolean, multieq::MultiEq, uint32::UInt32};
 use crate::{ConstraintSystem, SynthesisError};
 use ff::ScalarEngine;
diff --git a/bellman/src/gadgets/boolean.rs b/bellman/src/gadgets/boolean.rs
index bbc0d30..e08974d 100644
--- a/bellman/src/gadgets/boolean.rs
+++ b/bellman/src/gadgets/boolean.rs
@@ -1,3 +1,5 @@
+//! Gadgets for allocating bits in the circuit and performing boolean logic.
+
 use ff::{BitIterator, Field, PrimeField, ScalarEngine};
 
 use crate::{ConstraintSystem, LinearCombination, SynthesisError, Variable};
diff --git a/bellman/src/gadgets/lookup.rs b/bellman/src/gadgets/lookup.rs
index 8124b22..b83844d 100644
--- a/bellman/src/gadgets/lookup.rs
+++ b/bellman/src/gadgets/lookup.rs
@@ -1,3 +1,5 @@
+//! Window table lookup gadgets.
+
 use ff::{Field, ScalarEngine};
 
 use super::boolean::Boolean;
diff --git a/bellman/src/gadgets/multipack.rs b/bellman/src/gadgets/multipack.rs
index 1fa1967..c0dc50e 100644
--- a/bellman/src/gadgets/multipack.rs
+++ b/bellman/src/gadgets/multipack.rs
@@ -1,3 +1,5 @@
+//! Helpers for packing vectors of bits into scalar field elements.
+
 use super::boolean::Boolean;
 use super::num::Num;
 use super::Assignment;
diff --git a/bellman/src/gadgets/num.rs b/bellman/src/gadgets/num.rs
index b7caf6d..8be5448 100644
--- a/bellman/src/gadgets/num.rs
+++ b/bellman/src/gadgets/num.rs
@@ -1,3 +1,5 @@
+//! Gadgets representing numbers in the scalar field of the underlying curve.
+
 use ff::{BitIterator, Field, PrimeField, PrimeFieldRepr, ScalarEngine};
 
 use crate::{ConstraintSystem, LinearCombination, SynthesisError, Variable};
diff --git a/bellman/src/gadgets/sha256.rs b/bellman/src/gadgets/sha256.rs
index a875513..0c8efea 100644
--- a/bellman/src/gadgets/sha256.rs
+++ b/bellman/src/gadgets/sha256.rs
@@ -1,3 +1,8 @@
+//! Circuits for the [SHA-256] hash function and its internal compression
+//! function.
+//!
+//! [SHA-256]: https://tools.ietf.org/html/rfc6234
+
 use super::boolean::Boolean;
 use super::multieq::MultiEq;
 use super::uint32::UInt32;
diff --git a/bellman/src/gadgets/test/mod.rs b/bellman/src/gadgets/test/mod.rs
index fedfe94..47392f1 100644
--- a/bellman/src/gadgets/test/mod.rs
+++ b/bellman/src/gadgets/test/mod.rs
@@ -1,3 +1,5 @@
+//! Helpers for testing circuit implementations.
+
 use ff::{Field, PrimeField, PrimeFieldRepr, ScalarEngine};
 
 use crate::{ConstraintSystem, Index, LinearCombination, SynthesisError, Variable};
diff --git a/bellman/src/gadgets/uint32.rs b/bellman/src/gadgets/uint32.rs
index cf8e390..a10be6c 100644
--- a/bellman/src/gadgets/uint32.rs
+++ b/bellman/src/gadgets/uint32.rs
@@ -1,3 +1,6 @@
+//! Circuit representation of a [`u32`], with helpers for the [`sha256`]
+//! gadgets.
+
 use ff::{Field, PrimeField, ScalarEngine};
 
 use crate::{ConstraintSystem, LinearCombination, SynthesisError};
diff --git a/bellman/src/groth16/mod.rs b/bellman/src/groth16/mod.rs
index 44c6f22..1ff152d 100644
--- a/bellman/src/groth16/mod.rs
+++ b/bellman/src/groth16/mod.rs
@@ -1,3 +1,7 @@
+//! The [Groth16] proving system.
+//!
+//! [Groth16]: https://eprint.iacr.org/2016/260
+
 use group::{CurveAffine, EncodedPoint};
 use pairing::{Engine, PairingCurveAffine};
 
diff --git a/bellman/src/lib.rs b/bellman/src/lib.rs
index 5152b0f..a3b577b 100644
--- a/bellman/src/lib.rs
+++ b/bellman/src/lib.rs
@@ -1,3 +1,137 @@
+//! `bellman` is a crate for building zk-SNARK circuits. It provides circuit
+//! traits and and primitive structures, as well as basic gadget implementations
+//! such as booleans and number abstractions.
+//!
+//! # Example circuit
+//!
+//! Say we want to write a circuit that proves we know the preimage to some hash
+//! computed using SHA-256d (calling SHA-256 twice). The preimage must have a
+//! fixed length known in advance (because the circuit parameters will depend on
+//! it), but can otherwise have any value. We take the following strategy:
+//!
+//! - Witness each bit of the preimage.
+//! - Compute `hash = SHA-256d(preimage)` inside the circuit.
+//! - Expose `hash` as a public input using multiscalar packing.
+//!
+//! ```
+//! use bellman::{
+//!     gadgets::{
+//!         boolean::{AllocatedBit, Boolean},
+//!         multipack,
+//!         sha256::sha256,
+//!     },
+//!     groth16, Circuit, ConstraintSystem, SynthesisError,
+//! };
+//! use pairing::{bls12_381::Bls12, Engine};
+//! use rand::rngs::OsRng;
+//! use sha2::{Digest, Sha256};
+//!
+//! /// Our own SHA-256d gadget. Input and output are in little-endian bit order.
+//! fn sha256d<E: Engine, CS: ConstraintSystem<E>>(
+//!     mut cs: CS,
+//!     data: &[Boolean],
+//! ) -> Result<Vec<Boolean>, SynthesisError> {
+//!     // Flip endianness of each input byte
+//!     let input: Vec<_> = data
+//!         .chunks(8)
+//!         .map(|c| c.iter().rev())
+//!         .flatten()
+//!         .cloned()
+//!         .collect();
+//!
+//!     let mid = sha256(cs.namespace(|| "SHA-256(input)"), &input)?;
+//!     let res = sha256(cs.namespace(|| "SHA-256(mid)"), &mid)?;
+//!
+//!     // Flip endianness of each output byte
+//!     Ok(res
+//!         .chunks(8)
+//!         .map(|c| c.iter().rev())
+//!         .flatten()
+//!         .cloned()
+//!         .collect())
+//! }
+//!
+//! struct MyCircuit {
+//!     /// The input to SHA-256d we are proving that we know. Set to `None` when we
+//!     /// are verifying a proof (and do not have the witness data).
+//!     preimage: Option<[u8; 80]>,
+//! }
+//!
+//! impl<E: Engine> Circuit<E> for MyCircuit {
+//!     fn synthesize<CS: ConstraintSystem<E>>(self, cs: &mut CS) -> Result<(), SynthesisError> {
+//!         // Compute the values for the bits of the preimage. If we are verifying a proof,
+//!         // we still need to create the same constraints, so we return an equivalent-size
+//!         // Vec of None (indicating that the value of each bit is unknown).
+//!         let bit_values = if let Some(preimage) = self.preimage {
+//!             preimage
+//!                 .into_iter()
+//!                 .map(|byte| (0..8).map(move |i| (byte >> i) & 1u8 == 1u8))
+//!                 .flatten()
+//!                 .map(|b| Some(b))
+//!                 .collect()
+//!         } else {
+//!             vec![None; 80 * 8]
+//!         };
+//!         assert_eq!(bit_values.len(), 80 * 8);
+//!
+//!         // Witness the bits of the preimage.
+//!         let preimage_bits = bit_values
+//!             .into_iter()
+//!             .enumerate()
+//!             // Allocate each bit.
+//!             .map(|(i, b)| {
+//!                 AllocatedBit::alloc(cs.namespace(|| format!("preimage bit {}", i)), b)
+//!             })
+//!             // Convert the AllocatedBits into Booleans (required for the sha256 gadget).
+//!             .map(|b| b.map(Boolean::from))
+//!             .collect::<Result<Vec<_>, _>>()?;
+//!
+//!         // Compute hash = SHA-256d(preimage).
+//!         let hash = sha256d(cs.namespace(|| "SHA-256d(preimage)"), &preimage_bits)?;
+//!
+//!         // Expose the vector of 32 boolean variables as compact public inputs.
+//!         multipack::pack_into_inputs(cs.namespace(|| "pack hash"), &hash)
+//!     }
+//! }
+//!
+//! // Create parameters for our circuit. In a production deployment these would
+//! // be generated securely using a multiparty computation.
+//! let params = {
+//!     let c = MyCircuit { preimage: None };
+//!     groth16::generate_random_parameters::<Bls12, _, _>(c, &mut OsRng).unwrap()
+//! };
+//!
+//! // Prepare the verification key (for proof verification).
+//! let pvk = groth16::prepare_verifying_key(&params.vk);
+//!
+//! // Pick a preimage and compute its hash.
+//! let preimage = [42; 80];
+//! let hash = Sha256::digest(&Sha256::digest(&preimage));
+//!
+//! // Create an instance of our circuit (with the preimage as a witness).
+//! let c = MyCircuit {
+//!     preimage: Some(preimage),
+//! };
+//!
+//! // Create a Groth16 proof with our parameters.
+//! let proof = groth16::create_random_proof(c, &params, &mut OsRng).unwrap();
+//!
+//! // Pack the hash as inputs for proof verification.
+//! let hash_bits = multipack::bytes_to_bits_le(&hash);
+//! let inputs = multipack::compute_multipacking::<Bls12>(&hash_bits);
+//!
+//! // Check the proof!
+//! assert!(groth16::verify_proof(&pvk, &proof, &inputs).unwrap());
+//! ```
+//!
+//! # Roadmap
+//!
+//! `bellman` is being refactored into a generic proving library. Currently it
+//! is pairing-specific, and different types of proving systems need to be
+//! implemented as sub-modules. After the refactor, `bellman` will be generic
+//! using the [`ff`] and [`group`] crates, while specific proving systems will
+//! be separate crates that pull in the dependencies they require.
+
 // Catch documentation errors caused by code changes.
 #![deny(intra_doc_link_resolution_failure)]
 
diff --git a/bellman/src/multicore.rs b/bellman/src/multicore.rs
index ff97e06..ba69b5f 100644
--- a/bellman/src/multicore.rs
+++ b/bellman/src/multicore.rs
@@ -1,8 +1,9 @@
-//! This is an interface for dealing with the kinds of
-//! parallel computations involved in bellman. It's
-//! currently just a thin wrapper around CpuPool and
-//! crossbeam but may be extended in the future to
-//! allow for various parallelism strategies.
+//! An interface for dealing with the kinds of parallel computations involved in
+//! `bellman`. It's currently just a thin wrapper around [`CpuPool`] and
+//! [`crossbeam`] but may be extended in the future to allow for various
+//! parallelism strategies.
+//!
+//! [`CpuPool`]: futures_cpupool::CpuPool
 
 #[cfg(feature = "multicore")]
 mod implementation {
diff --git a/ff/src/lib.rs b/ff/src/lib.rs
index 456cbc1..6be25da 100644
--- a/ff/src/lib.rs
+++ b/ff/src/lib.rs
@@ -1,3 +1,5 @@
+//! This crate provides traits for working with finite fields.
+
 // Catch documentation errors caused by code changes.
 #![deny(intra_doc_link_resolution_failure)]
 #![allow(unused_imports)]
diff --git a/pairing/src/bls12_381/mod.rs b/pairing/src/bls12_381/mod.rs
index 8fc6bbd..e6e88dd 100644
--- a/pairing/src/bls12_381/mod.rs
+++ b/pairing/src/bls12_381/mod.rs
@@ -1,3 +1,6 @@
+//! An implementation of the BLS12-381 pairing-friendly elliptic curve
+//! construction.
+
 mod ec;
 mod fq;
 mod fq12;
diff --git a/pairing/src/lib.rs b/pairing/src/lib.rs
index 9f20a88..89e5873 100644
--- a/pairing/src/lib.rs
+++ b/pairing/src/lib.rs
@@ -1,3 +1,5 @@
+//! A library for working with pairing-friendly curves.
+
 // `clippy` is a code linting tool for improving code quality by catching
 // common mistakes or strange code patterns. If the `cargo-clippy` feature
 // is provided, all compiler warnings are prohibited.
diff --git a/zcash_client_backend/src/constants/mainnet.rs b/zcash_client_backend/src/constants/mainnet.rs
index 24dbbe7..f3f020d 100644
--- a/zcash_client_backend/src/constants/mainnet.rs
+++ b/zcash_client_backend/src/constants/mainnet.rs
@@ -1,3 +1,5 @@
+//! Constants for the Zcash main network.
+
 /// The mainnet coin type for ZEC, as defined by [SLIP 44].
 ///
 /// [SLIP 44]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
diff --git a/zcash_client_backend/src/constants/testnet.rs b/zcash_client_backend/src/constants/testnet.rs
index a83706e..5379d5a 100644
--- a/zcash_client_backend/src/constants/testnet.rs
+++ b/zcash_client_backend/src/constants/testnet.rs
@@ -1,3 +1,5 @@
+//! Constants for the Zcash test network.
+
 /// The testnet coin type for ZEC, as defined by [SLIP 44].
 ///
 /// [SLIP 44]: https://github.com/satoshilabs/slips/blob/master/slip-0044.md
diff --git a/zcash_primitives/src/block.rs b/zcash_primitives/src/block.rs
index 28a7441..ecb0e5b 100644
--- a/zcash_primitives/src/block.rs
+++ b/zcash_primitives/src/block.rs
@@ -1,3 +1,5 @@
+//! Structs and methods for handling Zcash block headers.
+
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use hex;
 use std::fmt;
diff --git a/zcash_primitives/src/block/equihash.rs b/zcash_primitives/src/block/equihash.rs
index 2a3bb66..5d40465 100644
--- a/zcash_primitives/src/block/equihash.rs
+++ b/zcash_primitives/src/block/equihash.rs
@@ -1,3 +1,7 @@
+//! Verification functions for the [Equihash] proof-of-work algorithm.
+//!
+//! [Equihash]: https://zips.z.cash/protocol/protocol.pdf#equihash
+
 use blake2b_simd::{Hash as Blake2bHash, Params as Blake2bParams, State as Blake2bState};
 use byteorder::{BigEndian, LittleEndian, ReadBytesExt, WriteBytesExt};
 use log::error;
diff --git a/zcash_primitives/src/constants.rs b/zcash_primitives/src/constants.rs
index 39d55f3..37d337d 100644
--- a/zcash_primitives/src/constants.rs
+++ b/zcash_primitives/src/constants.rs
@@ -1,3 +1,5 @@
+//! Various constants used by the Zcash primitives.
+
 /// First 64 bytes of the BLAKE2s input during group hash.
 /// This is chosen to be some random string that we couldn't have anticipated when we designed
 /// the algorithm, for rigidity purposes.
diff --git a/zcash_primitives/src/group_hash.rs b/zcash_primitives/src/group_hash.rs
index 8549c5e..6aac847 100644
--- a/zcash_primitives/src/group_hash.rs
+++ b/zcash_primitives/src/group_hash.rs
@@ -1,3 +1,7 @@
+//! Implementation of [group hashing into Jubjub][grouphash].
+//!
+//! [grouphash]: https://zips.z.cash/protocol/protocol.pdf#concretegrouphashjubjub
+
 use crate::jubjub::{edwards, JubjubEngine, PrimeOrder};
 
 use ff::PrimeField;
diff --git a/zcash_primitives/src/jubjub/mod.rs b/zcash_primitives/src/jubjub/mod.rs
index 40938f3..4998a0b 100644
--- a/zcash_primitives/src/jubjub/mod.rs
+++ b/zcash_primitives/src/jubjub/mod.rs
@@ -1,3 +1,6 @@
+//! The [Jubjub] curve for efficient elliptic curve operations in circuits built
+//! over [BLS12-381].
+//!
 //! Jubjub is a twisted Edwards curve defined over the BLS12-381 scalar
 //! field, Fr. It takes the form `-x^2 + y^2 = 1 + dx^2y^2` with
 //! `d = -(10240/10241)`. It is birationally equivalent to a Montgomery
@@ -16,6 +19,9 @@
 //! It is a complete twisted Edwards curve, so the equivalence with
 //! the Montgomery curve forms a group isomorphism, allowing points
 //! to be freely converted between the two forms.
+//!
+//! [Jubjub]: https://zips.z.cash/protocol/protocol.pdf#jubjub
+//! [BLS12-381]: pairing::bls12_381
 
 use ff::{Field, PrimeField, SqrtField};
 use pairing::Engine;
diff --git a/zcash_primitives/src/keys.rs b/zcash_primitives/src/keys.rs
index 8c8a4b1..76914ba 100644
--- a/zcash_primitives/src/keys.rs
+++ b/zcash_primitives/src/keys.rs
@@ -1,6 +1,8 @@
 //! Sapling key components.
 //!
-//! Implements section 4.2.2 of the Zcash Protocol Specification.
+//! Implements [section 4.2.2] of the Zcash Protocol Specification.
+//!
+//! [section 4.2.2]: https://zips.z.cash/protocol/protocol.pdf#saplingkeycomponents
 
 use crate::{
     jubjub::{edwards, FixedGenerators, JubjubEngine, JubjubParams, ToUniform, Unknown},
diff --git a/zcash_primitives/src/lib.rs b/zcash_primitives/src/lib.rs
index e8c2a51..713ca2b 100644
--- a/zcash_primitives/src/lib.rs
+++ b/zcash_primitives/src/lib.rs
@@ -1,3 +1,8 @@
+//! *General Zcash primitives.*
+//!
+//! `zcash_primitives` is a library that provides the core structs and functions necessary
+//! for working with Zcash.
+
 // Catch documentation errors caused by code changes.
 #![deny(intra_doc_link_resolution_failure)]
 
diff --git a/zcash_primitives/src/pedersen_hash.rs b/zcash_primitives/src/pedersen_hash.rs
index 835e9c7..690e977 100644
--- a/zcash_primitives/src/pedersen_hash.rs
+++ b/zcash_primitives/src/pedersen_hash.rs
@@ -1,3 +1,5 @@
+//! Implementation of the Pedersen hash function used in Sapling.
+
 use crate::jubjub::*;
 use ff::{Field, PrimeField, PrimeFieldRepr};
 
diff --git a/zcash_primitives/src/primitives.rs b/zcash_primitives/src/primitives.rs
index a336673..af4fa3a 100644
--- a/zcash_primitives/src/primitives.rs
+++ b/zcash_primitives/src/primitives.rs
@@ -1,3 +1,5 @@
+//! Structs for core Zcash primitives.
+
 use ff::{Field, PrimeField, PrimeFieldRepr};
 
 use crate::constants;
diff --git a/zcash_primitives/src/redjubjub.rs b/zcash_primitives/src/redjubjub.rs
index 6721b5e..187ebd3 100644
--- a/zcash_primitives/src/redjubjub.rs
+++ b/zcash_primitives/src/redjubjub.rs
@@ -1,5 +1,7 @@
-//! Implementation of RedJubjub, a specialization of RedDSA to the Jubjub curve.
-//! See section 5.4.6 of the Sapling protocol specification.
+//! Implementation of [RedJubjub], a specialization of RedDSA to the Jubjub
+//! curve.
+//!
+//! [RedJubjub]: https://zips.z.cash/protocol/protocol.pdf#concretereddsa
 
 use crate::jubjub::{edwards::Point, FixedGenerators, JubjubEngine, JubjubParams, Unknown};
 use ff::{Field, PrimeField, PrimeFieldRepr};
diff --git a/zcash_primitives/src/transaction/components.rs b/zcash_primitives/src/transaction/components.rs
index c0410c4..270bac5 100644
--- a/zcash_primitives/src/transaction/components.rs
+++ b/zcash_primitives/src/transaction/components.rs
@@ -1,3 +1,5 @@
+//! Structs representing the components within Zcash transactions.
+
 use crate::jubjub::{edwards, Unknown};
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use ff::{PrimeField, PrimeFieldRepr};
diff --git a/zcash_primitives/src/transaction/mod.rs b/zcash_primitives/src/transaction/mod.rs
index 10e935b..4c203c5 100644
--- a/zcash_primitives/src/transaction/mod.rs
+++ b/zcash_primitives/src/transaction/mod.rs
@@ -1,3 +1,5 @@
+//! Structs and methods for handling Zcash transactions.
+
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
 use hex;
 use sha2::{Digest, Sha256};
diff --git a/zcash_primitives/src/zip32.rs b/zcash_primitives/src/zip32.rs
index 6cbc462..f346625 100644
--- a/zcash_primitives/src/zip32.rs
+++ b/zcash_primitives/src/zip32.rs
@@ -1,3 +1,7 @@
+//! Implementation of [ZIP 32] for hierarchical deterministic key management.
+//!
+//! [ZIP 32]: https://zips.z.cash/zip-0032
+
 use aes::Aes256;
 use blake2b_simd::Params as Blake2bParams;
 use byteorder::{ByteOrder, LittleEndian, ReadBytesExt, WriteBytesExt};
diff --git a/zcash_proofs/src/circuit.rs b/zcash_proofs/src/circuit.rs
index ac7e74c..6d26fa4 100644
--- a/zcash_proofs/src/circuit.rs
+++ b/zcash_proofs/src/circuit.rs
@@ -1,3 +1,5 @@
+//! Implementations of the Zcash circuits and Zcash-specific gadgets.
+
 pub mod ecc;
 pub mod pedersen_hash;
 
diff --git a/zcash_proofs/src/circuit/ecc.rs b/zcash_proofs/src/circuit/ecc.rs
index fa4913a..e65d0ed 100644
--- a/zcash_proofs/src/circuit/ecc.rs
+++ b/zcash_proofs/src/circuit/ecc.rs
@@ -1,3 +1,5 @@
+//! Gadgets implementing Jubjub elliptic curve operations.
+
 use ff::Field;
 use pairing::Engine;
 
diff --git a/zcash_proofs/src/circuit/pedersen_hash.rs b/zcash_proofs/src/circuit/pedersen_hash.rs
index 409f30e..15cc0c9 100644
--- a/zcash_proofs/src/circuit/pedersen_hash.rs
+++ b/zcash_proofs/src/circuit/pedersen_hash.rs
@@ -1,3 +1,5 @@
+//! Gadget for Zcash's Pedersen hash.
+
 use super::ecc::{EdwardsPoint, MontgomeryPoint};
 use bellman::gadgets::boolean::Boolean;
 use bellman::gadgets::lookup::*;
diff --git a/zcash_proofs/src/circuit/sapling.rs b/zcash_proofs/src/circuit/sapling.rs
index 08e55e6..aa4b7c8 100644
--- a/zcash_proofs/src/circuit/sapling.rs
+++ b/zcash_proofs/src/circuit/sapling.rs
@@ -1,3 +1,5 @@
+//! The Sapling circuits.
+
 use ff::{Field, PrimeField, PrimeFieldRepr};
 
 use bellman::{Circuit, ConstraintSystem, SynthesisError};
diff --git a/zcash_proofs/src/circuit/sprout/mod.rs b/zcash_proofs/src/circuit/sprout/mod.rs
index 959ec78..1877047 100644
--- a/zcash_proofs/src/circuit/sprout/mod.rs
+++ b/zcash_proofs/src/circuit/sprout/mod.rs
@@ -1,3 +1,15 @@
+//! The "hybrid Sprout" circuit.
+//!
+//! "Hybrid Sprout" refers to the implementation of the [Sprout statement] in
+//! `bellman` for [`groth16`], instead of the [original implementation][oldimpl]
+//! using [`libsnark`] for [BCTV14].
+//!
+//! [Sprout statement]: https://zips.z.cash/protocol/protocol.pdf#joinsplitstatement
+//! [`groth16`]: bellman::groth16
+//! [oldimpl]: https://github.com/zcash/zcash/tree/v2.0.7/src/zcash/circuit
+//! [`libsnark`]: https://github.com/scipr-lab/libsnark
+//! [BCTV14]: https://eprint.iacr.org/2013/879
+
 use bellman::gadgets::boolean::{AllocatedBit, Boolean};
 use bellman::gadgets::multipack::pack_into_inputs;
 use bellman::{Circuit, ConstraintSystem, LinearCombination, SynthesisError};
diff --git a/zcash_proofs/src/lib.rs b/zcash_proofs/src/lib.rs
index a323cc3..0a1f9f2 100644
--- a/zcash_proofs/src/lib.rs
+++ b/zcash_proofs/src/lib.rs
@@ -1,3 +1,8 @@
+//! *Zcash circuits and proofs.*
+//!
+//! `zcash_proofs` contains the zk-SNARK circuits used by Zcash, and the APIs for creating
+//! and verifying proofs.
+
 // Catch documentation errors caused by code changes.
 #![deny(intra_doc_link_resolution_failure)]
 
diff --git a/zcash_proofs/src/sapling/mod.rs b/zcash_proofs/src/sapling/mod.rs
index 9aa62f1..60ffd9b 100644
--- a/zcash_proofs/src/sapling/mod.rs
+++ b/zcash_proofs/src/sapling/mod.rs
@@ -1,3 +1,5 @@
+//! Helpers for creating Sapling proofs.
+
 use pairing::bls12_381::Bls12;
 use zcash_primitives::jubjub::{
     edwards, fs::FsRepr, FixedGenerators, JubjubBls12, JubjubParams, Unknown,