Kinase suppressor of Ras (KSR) is a conserved component of the Ras pathway that functions as a molecular scaffold to enhance signaling between the core kinase components of the ERK cascade--Raf, MEK, and ERK. KSR interacts constitutively with MEK and translocates from the cytosol to the plasma membrane on Ras activation. At the membrane, KSR coordinates the assembly of a multiprotein complex containing Raf, MEK, and ERK and facilitates signal transmission from Raf to MEK and ERK. In this chapter, we will describe methods for assessing KSR function in response to Ras pathway activation. Protocols will be included that examine the ERK scaffolding activity and subcellular localization of KSR.