The advent of coupled earth system models has raised an important question in parallel computing: What is the most effective method for coupling many parallel models to form a high-performance coupled modeling system. We present our solution to this problem--The Model Coupling Toolkit (MCT). We explain how our effort to construct the Next-Generation Coupler for NCAR Community Climate System Model motivated us to create this toolkit. We describe in detail the conceptual design of the MCT and explain its usage in constructing parallel coupled models. We present preliminary performance results for the toolkit' parallel data transfer facilities. Finally, we outline an agenda for future development of the MCT.