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diff --git a/doc/mesh.rst b/doc/mesh.rst
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--- a/doc/mesh.rst
+++ b/doc/mesh.rst
@@ -8,6 +8,40 @@ Mesh management
 
 .. automodule:: meshmode.mesh
 
+Design of the Data Structure
+----------------------------
+
+Why does a :class:`Mesh` need to be broken into :class:`MeshElementGroup` instances?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Elements can be of different types (e.g. triangle, quadrilateral,
+tetrahedron, what have you). In addition, elements may vary in the
+polynomial degree used to represent them (see also below).
+
+All these bits of information could in principle be stored by element,
+but having large, internally homogeneous groups is a good thing from an
+efficiency standpoint. (So that you can, e.g., launch one GPU kernel to
+deal with all order-3 triangles, instead of maybe having to dispatch
+based on type and size inside the kernel)
+
+What is the difference between 'vertices' and 'nodes'?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Nodes exist mainly to represent the (potentially non-affine) deformation of
+each element, by a one-to-one correspondence with
+:attr:`MeshElementGroup.unit_nodes`.  They are unique to each element. Vertices
+on the other hand exist to clarify whether or not a point shared by two
+elements is actually identical (or just happens to be "close"). This is done by
+assigning (single, globally shared) vertex numbers and having elements refer to
+them.
+
+Consider the following picture:
+
+.. image:: images/nodes-vertices.png
+
+Mesh Data Structure
+-------------------
+
 .. autoclass:: MeshElementGroup
     :members:
     :undoc-members: