Software reuse enables developers to leverage past accomplishments and facilitates significant improvements in software productivity and quality. Software reuse catalyzes improvements in productivity by avoiding redevelopment and improvements in quality by incorporating components whose reliability has already been established. This study addresses a pivotal research issue that underlies software reuse - what factors characterize successful software reuse in large-scale systems. The research approach is to investigate, analyze, and evaluate software reuse empirically by mining software repositories from a NASA software development environment that actively reuses software. This software environment successfully follows principles of reuse-based software development in order to achieve an average reuse of 32 percent per project, which is the average amount of software either reused or modified from previous systems. We examine the repositories for 25 software systems ranging from 3,000 to 112,000 source lines from this software environment. We analyze four classes of software modules: modules reused without revision, modules reused with slight revision (<25 percent revision), modules reused with major revision (≥25 percent revision), and newly developed modules. We apply nonparametric statistical models to compare numerous development variables across the 2,954 software modules in the systems. We identify two categories of factors that characterize successful reuse-based software development of large-scale systems: module design factors and module implementation factors. We also evaluate the fault rates of the reused, modified, and newly developed modules. The module design factors that characterize module reuse without revision were (after normalization by size in source lines): few calls to other system modules, many calls to utility functions, few input-output parameters, few reads and writes, and many comments. The module implementation factors that characterize module reuse without revision were small size in source lines and (after normalization by size in source lines): low development effort and many assignment statements. The modules reused without revision had the fewest faults, fewest faults per source line, and lowest fault correction effor- t. The modules reused with major revision had the highest fault correction effort and highest fault isolation effort as wed as the most changes, most changes per source line, and highest change correction effort. In conclusion, we outline future research directions that build on these software reuse ideas and strategies.