This three-year Project Grant from the National Science Foundation's Division of Atmospheric and Geospace Sciences Geosciences program (CFDA 47.050) provides $426,760 to the University of Maryland, College Park to support collaborative research on electron heat flux regulation in the solar wind. The research aims to address the compelling science question of what regulates the solar wind heat flux by studying the relative importance of competing physical processes, including whistler heat-flux instabilities, binary collisions, and radial expansion effects. The grantee will use quasi-linear theory and kinetic theory of collisions in magnetized plasma to model the evolution of waves and electron heat flux in the radially varying solar wind. The theory will be driven by and tested against measurements from spacecraft between 0.3 and 1 AU of the solar wind electron distribution function, as well as proton parameters, magnetic field, and plasma wave data. The work supports the training of a graduate student and postdoctoral researcher.