Over the past decade there has been an increased demand for mixed-methods evaluations to better understand the complexity of international development interventions and in recognition of the fact that no single evaluation methodology can fully capture and measure the multiple processes and outcomes that every development program involves. At the same time, no consensus has been reached by policy makers and evaluation practitioners as to what exactly constitutes a mixed-methods approach. This SI Concept Note aims at helping that discussion by defining mixed-methods as evaluation approaches that systematically integrate quantitative and qualitative research methodologies at all stages of an evaluation. The paper further discusses the most important strengths and weaknesses of mixedmethods approaches compared to quantitative and qualitative only evaluations and lists a number of implementation challenges and ways to address them that may be useful to both producers and consumers of performance and impact evaluations.