This dissertation considers, in three parts, problems concerning mixing and chemical reactions in homogeneous turbulent flows. Direct numerical simulations of finite-rate chemical reactions occurring in moderate Reynolds number turbulence were used to provide data that are difficult to measure experimentally. In the first two parts, models for two phenomena contributing to unknown terms in statistical treatments of reacting flows are considered. In Part I models that are used in the solution of probability density function (pdf) equations are examined, whereas in Part II models used in moment methods for the mean reaction rate are evaluated. In Part III, results of the simulations were used to examine the structure of the reaction zone. (Abstract shortened with permission of author.)