Mixed methods in evaluation have the potential to enhance the credibility of evaluation and the outcomes of evaluation. This issue explores advances in understanding mixed methods in philosophical, theoretical, and methodological terms and presents specific illustrations of the application of these concepts in evaluation practice. Leading thinkers in the mixed methods evaluation community provide frameworks and strategies that are associated with improving the probability of reaching the goals of enhanced credibility for evaluations, the evidence they produce, and the actions taken as a result of the evaluation findings. This is the 138th volume of the Jossey-Bass quarterly report series New Directions for Evaluation, an official publication of the American Evaluation Association.