In electronic world, flip-flops and latches have been widely used. They can be used as storage devices to store state information, such as static memory. The flip-flops also can be made for counters, registers and other sequential control logic. In this book, we don’t discuss the components and configuration inside latches and flip-flops. However, we put more attention on how the latches and flip-flops change from one state to another state; how flip-flops work according to triggered edge of clock pulse; how the flip-flops and latches applications work. Meanwhile, we will step-by-step demonstrate how to use the simulation program (Quarter II) to simulate the circuits which are related with flip-flops and latches.. We also introduce some typical flip-flops applications, such as shift register, counter, and frequency divider, etc. This book provides many examples for students to fully understand each latch and flip-flop we mentioned, such as D flip-flop, S-R flip-flop, J-K flip-flop etc.