Ras family GTPases (RFGs), when in their active GTP-bound state, interact with a wide array of downstream effectors to regulate many biological functions in different cell types. How signal specificity among the closely related family members is achieved is still poorly understood. There is both promiscuity and specificity in the ability of RFGs to interact with and regulate the various effector families, as well as isoforms within those families. RFGs seem to have individual blueprints of effector interactions, and specificity should be considered in the context of the full spectrum of effectors they regulate. The sequencing of the genome has identified a remarkably diverse number of proteins with domains homologous to the Ras-binding domain (RBD) of known Ras effectors and, thus, with the potential to interact with Ras and/or other RFGs. In addition, other proteins without known RBD types are known to behave as RFG effectors, suggesting even more complexity in the number of effector interactions. Determining which of these many candidates are "true" effectors and characterizing their specificity is a critical step to understanding the specific signaling properties and biological functions of the various RFGs.