While improvement science has experienced a surge of interest over the past 30 years, applications of it are rare in the evaluation literature. This issue promotes the cross-fertilization of ideas, techniques, and tools between evaluation and improvement science. There are at least four areas where this cross-fertilization is particularly relevant: learning from error, examining variation, appreciating context, and focusing on systems change. This volume considers: the conceptual similarities and distinctions between improvement science and evaluation; the intellectual foundations, methods, and tools that collectively comprise improvement science; and case chapters that offer an inspiring review of state-of-the-art improvement science applications. Cutting across all of these applications is a shared grounding in systems thinking, a determination to capture and better understand variation and contextual complexity, as well as a sustained commitment to generative learning about projects and programs--all issues of great concern to evaluators. The issue offers producers and users of evaluations the potential benefits of a closer engagement with improvement science.This is the 153rd issue in the New Directions for Evaluation series from Jossey-Bass. It is an official publication ofthe American Evaluation Association.