The present invention relates to organic copolymers and organic semiconducting compositions comprising these materials, including layers and devices comprising such organic semiconductor compositions. The invention is also concerned with methods of preparing such organic semiconductor compositions and layers and uses thereof. The invention has application in the field of printed electronics and is particularly useful as the semiconducting material for use in formulations for organic thin film transistor (OTFT backplanes for displays, integrated circuits, organic light emitting diodes (OLEDs), photodetectors, organic photovoltaic (OPV) cells, sensors, memory elements and logic circuits.