This article reviews current progress in research in ferroelectric switching phenomena using in situ electron microscopy. We focus on state-of-the-art instrumentation, analytical methods, experimental procedures, and image contrast mechanisms. Particular emphasis is on ferroelectric domain and domain wall structures that determine ferroelectric behaviors. The applicability of in situ microscopy to studying a wide range of switching phenomena, such as domain nucleation, domain wall motion, and domain wall pinning by various types of defects, in ferroelectric thin films is demonstrated. The underlying physics of these dynamic processes is also discussed.