Fans of the science and industry of photonics are joiners, not loners. Usually because of the influence of one or two giants of industry or renowned academic institutions, clusters of like-minded enterprises sprout like mushrooms over particular geographical regions. Here we present the largest, best-represented areas of photonics expertise – judged mainly by the sheer number of contributing companies and institutions within a definable region. Optics Valley France Headquarters: Palaiseau Serves: France Founded: 1999 Members include: Renaud Lasers, Acces Vision, Thales Optronique. www.opticsvalley.org KAPID – Korea Association for Photonics Industry Development Headquarters: Gwangju Serves: South Korea Founded: 2000 Members include: 3i, Coset Inc., Symphony Energy Co. www.kapid.org Arizona Optics Industry Association Headquarters: Tucson Serves: Arizona’s “Optics Valley” Founded: 1992 Members include: Lowell Observatory, Zygo Corp., Kyocera Solar, NP Photonics Inc. www.aoia.org POPsud – OPTITEC Headquarters: Marseille Serves: Southern France Founded: 2000 Members include: Cilas, Horiba, Centre de Physique Théorique de l’Ecole Polytechnique www.popsud.org Optoelectronics Industry and Technology Development Association (OITDA) Headquarters: Tokyo Serves: Japan Founded: 1980 Members include: Sumitomo Electric Industries Ltd., Toshiba Corp., NEC Corp., Mitsubishi Electric Corp. www.oitda.or.jp Ontario Photonics Industry Network (inactive) Headquarters: Ottawa Served: Ontario province in Canada Members included: University of Ottawa Centre for Research in Photonics, Optiwave Systems Inc., Group IV Semiconductor. NB: Although the OPIN suspended operations recently, its 110+ member companies and institutions remain vital to the region. Optical Valley of China Headquarters: Wuhan Serves: China Founded: 2000 Members include: Yangtze Optical Fibre and Cable Co. Ltd., Huagong Laser Engineering Co. Ltd., HuaZhong University of Science and Technology. www.ovcexpo.com.cn South of England Photonics Network (SEPNET) Headquarters: Southampton, England Serves: Southern UK Founded: 1999; shuttered in 2001; restarted in 2007 Members include: Fianium Ltd., Bentham Instruments Ltd. www.sepnet.net New York Photonics Industry Association Headquarters: Rochester Serves: New York – includes Rochester Regional Photonics Group Members include: Bristol Instruments Inc., Cornell University Center for Materials Research, G-S Plastic Optics, Universal Photonics Inc. www.newyorkphotonics.org OpTec-Berlin-Brandenburg Headquarters: Berlin Serves: Berlin-Brandenburg region of Germany Founded: 2000 Members include: Bruker Nano GmbH, Holoeye Photonics AG, Optronik Berlin GmbH, TEC Microsystems AG. www.optecbb.de Honorable mentions: Taipei, Taiwan; Singapore; Thuringia, Germany; Scotland; Switzerland; the Aquitaine region of France; and the Bavaria region in Germany.