This paper introduces dynamic mechanism design in an elementary fashion. We first examine optimal dynamic mechanisms: We find necessary and sufficient conditions for perfect Bayesian incentive compatibility and formulate the optimal dynamic mechanism problem. We next examine efficient dynamic mechanisms: We establish the uniqueness of Groves mechanism and investigate budget balance of the dynamic pivot mechanism in some detail for a bilateral trading environment. This introduction reveals that many results and techniques of static mechanism design can be straightforwardly extended and adapted to the analysis of dynamic settings.