Two-phase flow and heat transfer is still an area of intense research and great uncertainty. Even severely restricting ourselves to just annular, internal two-phase flow does not significantly improve our chances of accurately predicting either pressure gradients or heat transfer coefficients for an arbitrary tube geometry or fluid. This article summarizes a series of investigations that aim to identify the fundamental governing physics of internal two-phase flow: a Theory of Everything. The techniques developed to do so have been varied, and novel approaches are presented here. At the macro scale, simultaneous visualization and measurement of pressure gradient have led to interesting observations about the relationship between flow regimes and these fundamental macroscale behaviors. Since the macroscale behaviors are governed, for the most part, by behaviors at the micro scale, a number of techniques have been developed to study this near-wall behavior in quantitative detail. In particular, dye-assisted planar laser induced fluorescence has provided the first accurate portrayals of the gas-liquid interface annular flow, and microscale multiphase particle image velocimetry has been used to obtain the velocity within the liquid film of annular flow from within micrometers of the wall to velocities within the waves 500 mu m or more from the wall. Statistical analyses of these data point toward a general approach for modeling wall shear in two-phase concurrent internal flow.