Edward J. Manser and Thomas Leung have collected the key techniques currently in use to probe the function of these ubiquitous proteins both in vitro and in vivo. Presented in a format that ensures ready reproducibility by accomplished experimentalists who have refined the various methods in their laboratories, each technique includes step-by-step instructions, tips on avoiding pitfalls and troubleshooting, and ancillary notes explaining how to adapt each procedure in the event of problems. The methods cover the spectrum of core techniques required for the five major GTPase subfamilies (Ras, Rho, Rab, Arf, and Ran) and permit a diversity of applications ranging from structural studies on a GTPase to real time in vivo analysis. Timely and highly practical, GTPase Protocols: The Ras Superfamily illuminates the powerful techniques used by investigators today to study this special family of proteins that plays such important roles in human health and disease.