Considerable research at DIII-D has been aimed at detailed comparisons of a variety of experimental fluctuation and turbulence measurements to turbulence simulations and theory. The goals of such comparisons are to improve the understanding of turbulence and transport as well as to test and provide feedback to the theory and simulations. Progress in this area will lead to confidence in the extrapolation of predictions to next-step fusion devices and, potentially, to improved control of transport. This paper summarizes some of the more recent and significant results of comparisons of experiment to theory and simulation that have been performed at DIII-D. These comparisons cover a range of plasma conditions (ohmic, L-mode, and impurity enhanced confinement), physical phenomena [transport, avalanches, zonal flows, and geodesic acoustic modes (GAMs)], and measurements (fluctuation levels, fluctuation spectra, radial correlation lengths, heat transport, and poloidal fluctuation velocity). Results reviewed here include comparisons between experimental turbulent radial correlation lengths and nonlinear turbulence simulations, measurements showing GAM activity (a type of zonal flow) similar to predictions, long-range or avalanche-type behavior with significant heat transport similar to that seen in nonlinear simulations, and reduction of turbulence with an enhancement of confinement during impurity injection similar to theory and simulation.