The purpose of this Guide is to provide education officials, program providers, and others seeking to sponsor a rigorous program evaluation with practical advice on finding a capable evaluator. More specifically, this Guide offers practical advice on finding an evaluator to conduct a rigorous evaluation to measure the effect of an educational program on outcomes such as student achievement. (Such evaluations are often called "impact" evaluations.) The Guide's main focus is on finding an evaluator to conduct a well-designed randomized controlled trial, since that is the primary type of evaluation capable of meeting the evidence standards of the What Works Clearinghouse of the U.S. Education Department's Institute of Education Sciences (IES). However, the Guide also includes endnotes in each section discussing how the principles might be adapted for those seeking to sponsor other high-quality evaluations when a randomized controlled trial is not feasible (e.g., well-matched comparison-group studies or regression-discontinuity studies). This Guide limits itself to key principles, and does not seek to be an exhaustive list of factors to consider in finding a capable evaluator. (Contains 8 notes.)