This actionable resource is intended to help funders adjust their practices to achieve more positive outcomes and greater social impact. The authors argue that foundations should use their endowments to make strategic mission (impact) investments that complement their grantmaking and leverage market forces. The article describes a variety of ways foundations can invest their endowments; explains how foundations can creatively leverage their investments to achieve desired social benefits; and advises funders that mission (or impact) investing requires both internal and external changes.