This book reviews the latest advancement of microfluidics and nanofluidics with a focus on electrokinetic phenomena in microfluidics and nanofluidics. It provides fundamental understanding of several new interfacial electrokinetic phenomena in microfluidics and nanofluidics. Chapter 1 gives a brief review of the fundamentals of interfacial electrokinetics. Chapter 2 shows induced charge electrokinetic transport phenomena. Chapter 3 presents the new advancement in DC dielectrophoresis. Chapter 4 introduces a novel nanofabrication method and the systematic studies of electrokinetic nanofluidics. Chapter 5 presents electrokinetic phenomena associated with Janus particles and Janus droplets. Chapter 6 introduces a new direction of electrokinetic nanofluidics: nanofluidic iontronics. Chapter 7 discusses an important differential resistive pulse sensor in microfluidics and nanofluidics.