Several methods for specifying boundary conditions at the limits of a regional model are compared. The methods investigated are those using clamped and radiation boundary conditions, one-way and two-way nesting in a model for a more extensive area, and "full" coupling based on domain decomposition techniques. These methods are compared in the realistic framework of interactions between a 1/15° model of the Bay of Biscay and a 1/3° model of the North Atlantic, over a 3-year simulation (1996-1998). The clamped and radiation boundary conditions systematically lead to energy accumulation and problematic recirculations along the boundary, and can disturb the internal dynamics of the regional domain. The one-way or two-way-nesting and the full-coupling methods result in far more satisfactory behaviour. For long periods of integration, the two-way mode improves both the fine and coarse-grid solutions. The full coupling method provides the most regular solution at the boundary, and also opens interesting new perspectives since it should enable the coupling of models with different physics. However it requires much more computation time.