Communication between cells is essential for all life processes. This is particularly evident for cells constituting the various tissues and organs in the body, to integrate and coordinate proper function. Channels or pores with the membranes of cells are an important mechanism for communication. Gap junctions are a unique type of channel interconnecting cells in all tissues in the body. Their importance has become evident with regard to diseases such as stroke and cancer. These diseases are reproduced in genetically altered mice lacking these specific channels, providing both understanding into these diseases, and tools for discovery of new therapeutic approaches.