Convection in stellar models

Convection has two main effects of interest to stellar modelers: It changes the stratification compared to a radiative or conductive region, and it mixes the matter efficiently. This was recognized early on, and a rudimentary description of convection was soon worked out this is the familiar mixing length formulation. This paper will compare and contrast this much used formulation with results from realistic 3D simulations of interacting convection and radiation in the surface layers of stars. Due to space limitations, this review will be concerned with convective envelopes, only.