Conducting implementation science research involves critical decision making on the methods for data collection and analysis as well as the study design that would best answer the research question of interest. This chapter reviews several research methods and study designs used in implementation science research. The chapter begins with an overview of qualitative, quantitative and mixed methods for identifying and/or assessing barriers and facilitators to implementing an evidence-based practice. The second part of the chapter looks at different study designs for carrying out studies to evaluate the effectiveness of different strategies to overcome barriers and harness facilitators. © 2024 selection and editorial matter, Per Nilsen; individual chapters, the contributors.