Retirement Issue Dedicated to Edward L. Clennan.

The enclosed is a special retirement issue of Photochemistry and Photobiology, dedicated to Edward L. Clennan. Papers are included by those with ties to Ed as former group members, collaborators, and colleagues. They cover a range of topics in photochemistry, photosensitization, photocatalysis, chemiluminescence, photorelease, helical compounds, and reactive intermediates, all of which are very fitting to Ed's contributions in fundamental science. His efforts include essential contributions to mechanisms of singlet oxygen in homogeneous and heterogeneous media, as well as photoinduced electron transfer reactions and photocyclizations to form helicenes. The latter topics also have potential use in organic electronic devices.