All life begins with a single cell. How can a community of cells—e.g., human tissues, microbial biofilms, and cancerous tumors—produce collective properties not shared by any one individual? Understanding how cells communicate is critical to understanding this developmental process of unguided design. Communication arises from the combination of genetic programming within cells and physical interactions between cells that result in their arrangement in space and time. Dissecting this interplay will grant insights into the fundamental forces that shape life on Earth, from bacteria to humans.