  We develop a tool akin to the revelation principle for dynamic
mechanism-selection games in which the designer can only commit to short-term
mechanisms. We identify a canonical class of mechanisms rich enough to
replicate the outcomes of any equilibrium in a mechanism-selection game between
an uninformed designer and a privately informed agent. A cornerstone of our
methodology is the idea that a mechanism should encode not only the rules that
determine the allocation, but also the information the designer obtains from
the interaction with the agent. Therefore, how much the designer learns, which
is the key tension in design with limited commitment, becomes an explicit part
of the design. Our result simplifies the search for the designer-optimal
outcome by reducing the agent's behavior to a series of participation,
truthtelling, and Bayes' plausibility constraints the mechanisms must satisfy.
