USAID's Private Sector Engagement (PSE) Policy recognizes that private sector resources and capabilities are required to work at the scale needed to address development challenges effectively and sustainably. Mobilizing private capital has become an increasingly important part of this effort. USAID's INVEST initiative has successfully engaged transaction advisors to mobilize over $800 million in investment capital for renewable energy, agriculture, financial services, and other priorities. Based on INVEST's experience, this learning brief describes how transaction advisory services can be used to address donor priorities and offers practical guidance on the design and management of programs using transaction advisory services to facilitate private sector investment.