diff --git a/src/bindings.rs b/src/bindings.rs
index bd4c1f8..abcb6f2 100644
--- a/src/bindings.rs
+++ b/src/bindings.rs
@@ -46,6 +46,7 @@ pub struct MfModel {
     pub q: *const c_float,
 }
 
+/// Loss functions.
 #[repr(C)]
 #[derive(Clone, Copy)]
 pub enum Loss {
diff --git a/src/error.rs b/src/error.rs
index 46f0c2e..96dccb1 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -2,6 +2,7 @@ use std::error;
 use std::ffi::NulError;
 use std::fmt;
 
+/// An error.
 #[derive(Debug, Eq, PartialEq)]
 pub enum Error {
     Io,
diff --git a/src/matrix.rs b/src/matrix.rs
index 132ea4e..9e7aab1 100644
--- a/src/matrix.rs
+++ b/src/matrix.rs
@@ -1,20 +1,24 @@
 use crate::bindings::{MfNode, MfProblem};
 
+/// A matrix.
 pub struct Matrix {
     data: Vec<MfNode>,
 }
 
 impl Matrix {
+    /// Creates a new matrix.
     pub fn new() -> Self {
         Self { data: Vec::new() }
     }
 
+    /// Creates a new matrix with a minimum capacity.
     pub fn with_capacity(capacity: usize) -> Self {
         Self {
             data: Vec::with_capacity(capacity),
         }
     }
 
+    /// Adds a value to the matrix.
     pub fn push(&mut self, row_index: i32, column_index: i32, value: f32) {
         assert!(row_index >= 0);
         assert!(column_index >= 0);
diff --git a/src/model.rs b/src/model.rs
index 043faa0..47d5a3d 100644
--- a/src/model.rs
+++ b/src/model.rs
@@ -4,6 +4,7 @@ use std::ffi::CString;
 use std::path::Path;
 use std::slice::Chunks;
 
+/// A model.
 #[derive(Debug)]
 pub struct Model {
     pub(crate) model: *mut MfModel,
diff --git a/src/params.rs b/src/params.rs
index 975ea7e..e417317 100644
--- a/src/params.rs
+++ b/src/params.rs
@@ -1,6 +1,7 @@
 use crate::bindings::*;
 use crate::{Error, Loss, Matrix, Model};
 
+/// A set of parameters.
 pub struct Params {
     param: MfParameter,
 }