25 years after the discovery of modular protein binding domains, we are now appreciating the critical role they play in the function and evolution of cell signalling networks. Modularity is a recurrent theme in signalling, operating across multiple scales, and understanding modular design principles is essential for the rational manipulation of signalling to improve human health. For more than a decade, a vibrant research community has gathered periodically in Seefeld, Austria, to discuss the latest developments in modularity in signalling. #EMBOmodularity