Book excerpt: Electrokinetics is currently the mechanism of choice for fluid actuation and bioparticle manipulation at microscale and nanoscale dimensions. There has recently been widespread interest in the use of AC electric fields, given the many advantages it offers over DC electrokinetics. Nevertheless, a fundamental understanding of the governing mechanisms underlying the complex and nonlinear physicochemical hydrodynamics associated with these systems is required before practical microfluidic and nanofluidic devices can be engineered. This text aims to provide a comprehensive treatise on both classical equilibrium electrokinetic phenomena as well as the more recent non-equilibrium phenomena associated with both DC and AC electrokinetics in the context of their application to the design of microfluidic and nanofluidic technology. In particular, Leslie Yeo and Hsueh-Chia Chang discuss the linear and nonlinear theories underlying electroosmosis, electrophoresis, and dielectrophoresis pertaining to electrolytes as well as dielectric systems. Interfacial electrokinetic phenomena such as electrospraying, electrospinning, and electrowetting are also discussed.