A new class of microgrids, called provisional microgrids, is introduced in this paper. Provisional microgrids hold similar characteristics as microgrids, however, do not possess the islanding capability and are dependent on one or more electrically connected microgrids for islanding purposes. Removing the islanding requirements and relying on the available unused capacity of existing microgrids, characterizes provisional microgrids as enablers of rapidly deploying variable generation renewable energy resources in distribution networks and further preventing underutilization of capital-intensive distributed energy resources (DERs) in microgrids. Provisional microgrids are defined and an uncertainty-constrained optimal scheduling model is developed which considers prevailing uncertainties associated with loads, non-dispatchable generation, and market price forecasts, as well as islanding incidents and the available unused capacity from coupled microgrids. The optimal scheduling problem is decomposed using Benders decomposition and solved via the robust optimization method. Numerical simulations study a test provisional microgrid for exploring its economic, reliability, and environmental merits.