During the latest decade we have worked on periodic surfaces with zero average
curvature and their significance in chemical structures, ranging from atomic and
molecular arrangements in crystals to complex self-assembled colloidal
aggregates. This approach has proved to be fruitful, not only in the
determination of complex structures, but also in the understanding of phase
behaviour and relations between structure and physical properties. Our aim has
been to summarise our own understanding of this growing field, and to provide
a complete description of relevant shapes and the forces behind their formation.