The high T c superconducting oxycarbonates form a large class whose crystal chemistry is presented herein. In the form of bulk materials, five families of oxycarbonates, involving lanthanides, thallium, bismuth, lead and mercury, have been synthesized with T c values up to 80 K. Laser ablation appears to be a very promising new soft chemistry method to synthesize new oxycarbonates in the form of thin films. This is illustrated by the phases (CaCuO 2 ) m , and (Ba 2 CuO 2 CO 3 ) n , that exhibit T c values up to 100 K.