The present experimental study of a transverse jet discharging into a supersonic nozzle was undertaken to clarify the details of the flow. Results of wall and impact pressure measurements throughout the core of the interaction field, as well as flow visualization tests, are reported for 11 tests differing as systematically as possible by the injected mass rate, injection station Mach number, and primary to secondary stagnation pressure ratio. These measurements are used in an effort to reconstruct the true structure of the flow and suggest the following characteristic features of it. The penetration and turning of the secondary (supersonic) jet is governed by the dynamics of the shock structure occurring in the free-expansion plume and it is not a simple function of jet momentum. The mixing region downstream of injection contains a "horseshoe" vortex separating the inner (jet) flow from the outer (freestream) flow near the nozzle wall. The entire interaction region is enveloped by a nearly ogival shock, the gross properties of which, to the first approximation, depend (nonlinearly) on the injected momentum, the freestream pressure, and the freestream velocity at the injection station.