The current structural data available on distinct serine/threonine protein kinases have been outlined. It also includes description of how kinases bind substrates at the active site, focusing on the P+1 pocket, which is remodeled in inactive forms of several protein kinases. Other topics tackled include substrate docking interactions outside the active site observed in mitogen-activated protein (MAP) kinases, cyclin dependent kinases (CDKs), and AGC kinases and how specificity among these different families of kinases is achieved from the organization of the binding site.