Software reuse is an important and relatively new approach to software engineering. The aim is further development of a methodology and mathematical theory of software metrics for evaluation of software reusability. In the second section, going after Introduction, it is demonstrated that reusability is a form of usability. This allows one to use experience in the development and utilization of software usability metrics for the development and utilization of software reuse metrics. In the third section, different types and classes of software metrics are explicated and compared, while in the fourth section, software metrics and their properties in a formalized context are studied. The research is oriented at the advancement of software engineering and, in particular, at creation of more efficient reuse metrics.