Stephen Cohen has studied the mechanisms that organise spatial pattern and control growth during animal development. Although focused mainly on insect appendage development, his work has provided important insights into processes fundamental to animal development. Among these was the finding that compartment boundaries serve as patterning centres by producing gradients of secreted signalling proteins. These morphogenetic gradients instruct cells about their fate as a function of their position. He has also studied how morphogen gradients contribute to size control. Recent work has focused on microRNAs as regulators of tissue growth and metabolism with emphasis on their roles in disease.