The method of numerical simulation has been used here to establish the heat transfer characteristics of a fluid jet impinging on a target surface. In particular, it was demonstrated that a fluid mechanic phenomenon designated as jet axis switching has a tremendous effect on both the magnitude and surface distribution of the impingement heat transfer coefficient. The neglect of this phenomenon, which has been common in the literature on jet impingement heat transfer, gives rise to significant inaccuracies in the predicted values of the heat transfer coefficient. As an essential prelude to the heat transfer analysis, the fluid mechanics of jet impingement were set forth in detail in order to document the jet-axis switching phenomenon. For this purpose, color contour and velocity vector diagrams are displayed to show the change of shape experienced by the jet as it passes through an unconfined space. The local heat transfer coefficient at all points of the impingement plate was determined. The highest values of the Nusselt number do not occur when the plate is nearest to the origin of the jet. Off-axis peaks of the local Nusselt number were found to exist at locations between z/b = 0 and 3 for respective impingement plate positions Xmax/b = 30 and 10. The numerical predictions compared favorably with experimental results from the literature.