diff --git a/src/distancematrix.rs b/src/distancematrix.rs
new file mode 100644
index 0000000..ababc55
--- /dev/null
+++ b/src/distancematrix.rs
@@ -0,0 +1,20 @@
+//! A distance matrix is stored as a list of taxon names, together with a square
+//! or triangular matrix representing all pairwise distances.
+
+/// The type of the matrix. Either square, lower triangular (excluding the
+/// diagonal), or upper triangular (excluding the diagonal).
+/// Square matrices are assumed to be symmetric, but this is not enforced nor checked.
+#[derive(Debug, PartialEq, Eq)]
+pub enum MatrixType {
+    Square,
+    Lower,
+    Upper,
+}
+
+/// A distance matrix containing a list of taxon names and a matrix of pairwise distances.
+#[derive(Debug)]
+pub struct DistanceMatrix {
+    names: Vec<String>,
+    distances: Vec<Vec<f32>>,
+    matrix_type: MatrixType,
+}
diff --git a/src/lib.rs b/src/lib.rs
index 592a248..add8ba2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,6 +12,7 @@ extern crate petgraph;
 
 pub mod alignment;
 pub mod annot;
+pub mod distancematrix;
 pub mod genome;
 #[cfg(feature = "phylogeny")]
 pub mod phylogeny;