Against the background of declining performance persistence in Private Equity, I argue that investors are - more than ever - forced to review the organizational and strategic aspects of PE firms. However, academic research yet provided little attention to the heterogeneity among PE-firms. This dissertation investigates three sources of heterogeneity among PE firms, namely: governance structures, investment strategies and human capital. Overall, I observe a significant impact of PE firm heterogeneity on investment returns. I find governance structures to severely influence deal-level divestment decisions. This particularly applies to those PE firms with a lack of reputation and during times of fundraising. Further, I find a significant impact of investment strategies on returns. I find evidence for the existence of a concave, U-shaped relationship between specialization and deal performance, in which the marginal benefits of specialization are positive at low levels of specialization and negative at high levels. I also investigate the impact of Operating Partner deal involvement on returns. I find considerable heterogeneity in the effect of Operating Partner involvement across different industries. A positive association between Operating Partner involvement and deal returns seems to be particularly prevalent for portfolio companies within volatile (or risky) industries.