Impact venture capital is an emerging financial sector focusing on investments in for-profit companies working on developing and commercializing technologies, processes, or products with positive environmental, social, and economic outcomes. Impact venture capitalists use various financial tools and provide sustainable entrepreneurs with resources unique to venture capital, such as mentorship, networking, and technical assistance. This chapter discusses the “impact start-up” financial market and the place for venture capital in the broader domain of sustainable investment and impact investing. It covers the core activities for the practice of impact venture capital and the different roles that venture capitalists assume in their relationships with investees. The chapter also examines the challenges that must be overcome for the impact venture capital sector to fulfill its promise as an important contributor to achieving society’s aspirations for sustainable development and progress.