To researchers of homogeneous olefin polymerization catalysts and to the broader catalysis community. This work systematically explores the process of constructing quantitative structure activity relationships (QSARs) to predict rate constants of various reaction steps from catalyst structure. Specifically, this work describes how to construct accurate and broadly applicable QSARs by fitting quantum chemistry calculations to experimental data. The focus is on Ti and Zr homogeneous olefin polymerization catalysts containing mixed cyclopentadienyl/aryloxide ligation. Polyolefins are widely used to make plastic bottles such as the ones pictured on this cover. The basic principles developed here extend to all kinds of catalysts. A major focus of this PhD dissertation is the use of QSARs to understand fundamental reaction mechanisms and to design catalysts with higher reactivity and selectivity. In many cases, orders of magnitude improvement in catalyst performance can be obtained.