Artist trading cards (ATCs) is a conceptual art project initiated by the Swiss artist M. Vänçi Stirnemann in 1997. He called it a Collaborative Cultural Performance. Artist trading cards are 2+1⁄2 by 3+1⁄2 inches (64 mm × 89 mm) in size, the same format as modern trading cards (hockey cards or baseball cards). They are self-made unique works or small series, signed and dated on the reverse by the artist/producer, exchanged and collected by the people who participate in the collaborative performance.