Rho-kinase (EC 2.7.11.1) is a serine/threonine kinase belonging to the AGC-family of protein kinases, originally identified as the first downstream effector of the small GTPase Rho. There are two Rho-kinase members, Rho-kinase α/ROCK2/ROKα and Rho-kinase β/ROCK1/ROKβ; both Rho-kinases are composed of an N-terminal catalytic domain, a central coiled-coil domain, and a C-terminal PH domain interrupted by a Cys-rich region. Rho-family small GTPases, such as Rho, Rac, and Cdc42, mediate a broad range of cellular responses that involve the actin cytoskeleton. Rhoregulates stress fiber formation and cell contraction, whereas Rac and Cdc42 regulate the formation of lamellipodia and filopodia, respectively, and promote protrusive activities. Rho-family GTPases also modulate microtubule dynamics and cell polarity. Furthermore, Rho-kinase is involved in smooth muscle contraction and actin organization, cell migration, neuronal architecture and neurite elongation, and cytokenesis, among several other functions.