The Reykjanes Ridge is a major topographic feature that lies south of Iceland in the North- Atlantic Ocean and strongly influences the Subpolar Gyre (SPG) circulation. Based on velocity and hydrographic measurements carried out along the crest of the Ridge from the Icelandic continental shelf to 50°N during the RREX cruise in June-July 2015, we derived the first direct estimates of volume and water masses transports over the Ridge. The circulation was mainly westward north of 53.35°N and eastward south of it. The westward transport was estimated at 21.9 ± 2.5 Sv (Sv = 10 6 m 3 s -1 ) and represents the SPG intensity. The westward flows followed two main pathways at 57°N near Bight Fracture Zone and at 59 – 62°N. We argue that those pathways were respectively connected to the northern branch of the North Atlantic Current and to the Sub-Arctic Front that were intersected by the southern part of the section. In addition to this horizontal circulation, mixing and bathymetry shaped the water mass distribution. Water mass transformations in the Iceland Basin lead to the formation of weakly stratified SubPolar Mode Water (SPMW). We explain why SPMW, which was the main contributor in terms of water mass to the westward flow, was denser at 57°N than at 59–62°N along the Ridge. At higher densities, both Intermediate Water, defined by a dissolved oxygen minimum, and Icelandic Slope Water contributed as much to the westward transport across the Ridge as the sum of Labrador Sea Water and Iceland-Scotland Overflow Water.