This guide provides a framework for ex-ante evaluation of fisheries and aquaculture projects in developing countries. Ex-ante impact evaluations check the potential of a project or program to deliver benefits from proposed interventions. Providing extensive annotated literature citations, this guide is designed for use by practitioners who may not be fisheries or aquaculture specialists. The guide uses concepts from results-based management, organized into five modules that structure the investigation and provide insights regarding alignment of the proposed intervention with stakeholder interests, feasibility of design, potential constraints to implementation, possible impact pathways and distributional effects of the intervention. Separately published case studies of investments in Bangladesh, Malawi and Ghana illustrate application of the guide.