Introduction: Appraising the quality of studies included in systematic reviews combining qualitative, quantitative and mixed methods studies is challenging. To address this challenge, a critical appraisal tool was developed: the Mixed Methods Appraisal Tool (MMAT). The aim of this paper is to present the MMAT. Development: The MMAT was developed in 2006 and was subject to pilot and interrater reliability testing. A revised new version of the MMAT was developed using the results from usefulness testing as well as a literature review on critical appraisal tools and a modified e-Delphi study with methodological experts to identify the core relevant criteria to include in the MMAT. Tool description: The MMAT includes quality criteria of five categories of study designs: (a) qualitative, (b) randomized controlled trial, (c) nonrandomized, (d) quantitative descriptive and (e) mixed methods studies. The MMAT focuses on core relevant methodological criteria and has five criteria per category of study design. Conclusion: The MMAT offers an alternative solution by proposing a unique tool that can appraise the quality of different study designs. Also, by limiting to core criteria, the MMAT can provide a more time efficient appraisal.