Wikipedia:

Photokina is the world's largest trade fair for the photographic and imaging industries. The first Photokina was held in Cologne, Germany, in 1950, and it is now held biennially in September at the koelnmesse Trade Fair and Exhibition Centre. Many photographic and imaging companies introduce and showcase state of the art imaging products at Photokina. Since 2004 there is another competing industry convention, the US based PMA trade show.