diff --git a/scico/linop/xray/_xray.py b/scico/linop/xray/_xray.py
index 75f035af..5e9caa61 100644
--- a/scico/linop/xray/_xray.py
+++ b/scico/linop/xray/_xray.py
@@ -235,6 +235,11 @@ def _calc_weights(
 class XRayTransform3D(LinearOperator):
     r"""General-purpose, 3D, parallel ray X-ray projector.
 
+    This projector approximates cubical voxels projecting onto
+    rectangular pixels and provides a back projector that is the true
+    adjoint of the forward projector. It is written purely in JAX,
+    allowing it to run on either CPU or GPU and minimizing host copies.
+
     Warning: This class is experimental and may be up to ten times slower
     than :class:`scico.linop.xray.astra.XRayTransform3D`.