Using a unique sample from the Longitudinal Research Database (LRD) of the U.S. Census Bureau, we study several related questions regarding the efficiency gains generated by venture capital (VC) investment in private firms. First, does VC backing improve the efficiency (total factor productivity, TFP) of private firms, and are certain kinds of VCs (higher reputation versus lower reputation) better at generating such efficiency gains than others? Second, how are such efficiency gains generated: Do venture capitalists invest in more efficient firms to begin with (screening) or do they improve efficiency after investment (monitoring)? Third, how are these efficiency gains spread out over rounds subsequent to VC investment? Fourth, what are the channels through which such efficiency gains are generated: increases in product market performance (sales) or reductions in various costs (labor, materials, total production costs)? Finally, how do such efficiency gains affect the probability of a successful exit (IPO or acquisition)? Our main findings are as follows. First, the overall efficiency of VC backed firms is higher than that of non-VC backed firms. Second, this efficiency advantage of VC backed firms arises from both screening and monitoring: the efficiency of VC backed firms prior to receiving financing is higher than that of non-VC backed firms and further, the growth in efficiency subsequent to receiving VC financing is greater for such firms relative to non-VC backed firms. Third, the above increase in efficiency of VC backed firms relative to non-VC backed firms increases over the first two rounds of VC financing, and remains at the higher level till exit. Fourth, while the TFP of firms prior to VC financing is lower for higher reputation VC backed firms, the increase in TFP subsequent to financing is significantly higher for the former firms, consistent with higher reputation VCs having greater monitoring ability. Fifth, the efficiency gains generated by VC backing arise primarily from improvement in product market performance (sales); however for higher reputation VCs, the additional efficiency gains arise from both an additional improvement in product market performance as well as from reductions in various input costs. Finally, both the level of TFP of VC backed firms prior to receiving financing and the growth in TFP subsequent to VC financing positively affect the probability of a successful exit (IPO or acquisition).