The chances of moving from the design of current US RTO/ISO-managed wholesale power markets to the Linked Swing-Contract Market Design would be enhanced if a means could be found to introduce the latter design in small transitional steps. Suppose a dispatchable resource m is a participant on day D in a US RTO/ISO managed day-ahead market (DAM), to be cleared using a standard SCUC/SCED optimization. This chapter describes, in general terms, an ISO-managed DAM that permits gradual transition to an SC DAM design. It shows how a standard analytical mixed integer linear programming (MILP) formulation for a DAM SCUC/SCED optimization can be modified in a minimally disruptive manner to provide an even playing field for participation by dispatchable resources offering simple types of swing contracts. This modified analytical MILP DAM formulation, referred to as the Transitional DAM, could thus constitute a first transitional step toward a full swing-contract DAM design.