[en] The hypothesis of stabilization of turbulence by shear in the E x B drift speed successfully predicts the observed turbulence reduction and confinement improvement seen at the L to H transition. This same hypothesis is the best explanation to date for the further confinement improvement seen in the plasma core when the plasma goes from H-mode to VH-mode. Consequently, the most fundamental question for H-mode studies now is: how is the electric field E_r formed? The radial force balance equation relates E_r to the main ion pressure gradient triangledown P_i, poloidal rotation ν_θi, and toroidal rotation ν_φi. In the plasma edge, direct measurements show triangledown P_i and ν_θi are the important terms at the L to H transition, with triangledown P_i being the dominant, negative term throughout most of the H-mode. Since E_r is observed to change prior to the change in triangledown P_i, the authors infer that main ion rotation, probably ν_θi, changes first, triggering the transition. E_r is seen to change prior to the change in fluctuations, consistent with E x B shear causing the change in fluctuations and transport. In the plasma core, E_r is primarily related to ν_φi. There is a clear temporal and spatial correlation between the change in E x B shear and the region of local confinement improvement when the plasma goes from H-mode to VH-mode. Direct manipulation of ν_φi and E x B shear using the drag produced by a non-axisymmetric magnetic perturbation has produced clear changes in local transport consistent with the E x B shear stabilization hypothesis. The implications of these results for theories of the L to H and H to VH transitions will be discussed. 83 refs., 5 figs