The formulation of analytical turbulence closure models for use in computational fluid mechanics is described. The subject of this chapter is the types of models that are used to predict the statistically averaged flow field – commonly known as Reynolds‐averaged Navier–Stokes equations (RANS) modeling. A variety of models are reviewed: these include two‐equation, eddy viscosity transport, and second moment closures. How they are formulated is not the main theme; it enters the discussion but the models are presented largely at an operational level. Several issues related to numerical implementation are discussed. Relative merits of the various formulations are commented on.