diff --git a/src/alsa_card.rs b/src/alsa_card.rs
index 9e3e47216..bf96f4a34 100644
--- a/src/alsa_card.rs
+++ b/src/alsa_card.rs
@@ -1,3 +1,10 @@
+//! Alsa audio subsystem.
+//!
+//! This mod mainly defines the `AlsaCard` struct, which is the only data
+//! structure interacting directly with the alsa library.
+//! No other struct should directly interact with the alsa bindings.
+
+
 use alsa::card::Card;
 use alsa::mixer::SelemChannelId::*;
 use alsa::mixer::{Mixer, Selem, SelemId};
diff --git a/src/support_alsa.rs b/src/support_alsa.rs
index 1fb85c95a..a4e30f7ba 100644
--- a/src/support_alsa.rs
+++ b/src/support_alsa.rs
@@ -1,3 +1,10 @@
+//! Alsa audio helper functions.
+//!
+//! This mod wraps around a few low-level alsa functions and abstracts
+//! out the details we don't care about. Mainly used by the
+//! [alsa_card mod](./alsa_card.html).
+
+
 use alsa::card::Card;
 use alsa::mixer::{Mixer, Selem, SelemId, Elem};
 use alsa;