Mixed methods research is a powerful approach for investigating complex processes and systems in health and healthcare. This article outlines integration principles and practices at three levels in mixed methods research: study design, methods, and interpretation and reporting. Integration at the study design level occurs through three basic designs—exploratory sequential, explanatory sequential, and convergent—and four advanced frameworks—multistage, intervention, case study, and participatory. Integration at the methods level occurs through four approaches: connecting, building, merging, and embedding. Integration at the interpretation and reporting level occurs through narrative, data transformation, and joint display. The fit of integration refers to the extent to which qualitative and quantitative findings cohere. Understanding these principles and practices can help health services researchers leverage the strengths of mixed methods. Mixed methods research combines quantitative and qualitative approaches to address complex research questions in health services. It is particularly useful for exploring why or how a phenomenon occurs, developing theories, or describing individual experiences. The integration of quantitative and qualitative data can enhance the value of mixed methods research by validating findings, generating samples, and informing the development of instruments or interventions. However, the extent to which mixed methods studies implement integration remains limited. Specific approaches to integrate qualitative and quantitative research procedures and data can be implemented at the design, methods, and interpretation and reporting levels. Integration at the study design level involves three basic designs and four advanced frameworks. Exploratory sequential designs begin with qualitative data collection, followed by quantitative data collection. Explanatory sequential designs begin with quantitative data collection, followed by qualitative data collection. Convergent designs collect and analyze qualitative and quantitative data simultaneously. Advanced frameworks include multistage, intervention, case study, and participatory designs. Integration at the methods level involves connecting, building, merging, and embedding. Connecting links data through sampling. Building informs data collection approaches. Merging brings data together for analysis. Embedding links data collection and analysis at multiple points. Integration at the interpretation and reporting level involves narrative, data transformation, and joint display. Narrative integrates findings through themes. Data transformation converts data into the other type for analysis. Joint display combines data visually to draw new insights. The "fit" of integration refers to the coherence of qualitative and quantitative findings. It can result in confirmation, expansion, or discordance. Examples illustrate integration practices in exploratory sequential and convergent designs. These examples show how integration can enhance understanding of complex health issues and improve the quality of health services research. The article concludes that mixed methods research offers a new framework for health services research with potential to generate unique insights into healthcare quality, access, and delivery.Mixed methods research is a powerful approach for investigating complex processes and systems in health and healthcare. This article outlines integration principles and practices at three levels in mixed methods research: study design, methods, and interpretation and reporting. Integration at the study design level occurs through three basic designs—exploratory sequential, explanatory sequential, and convergent—and four advanced frameworks—multistage, intervention, case study, and participatory. Integration at the methods level occurs through four approaches: connecting, building, merging, and embedding. Integration at the interpretation and reporting level occurs through narrative, data transformation, and joint display. The fit of integration refers to the extent to which qualitative and quantitative findings cohere. Understanding these principles and practices can help health services researchers leverage the strengths of mixed methods. Mixed methods research combines quantitative and qualitative approaches to address complex research questions in health services. It is particularly useful for exploring why or how a phenomenon occurs, developing theories, or describing individual experiences. The integration of quantitative and qualitative data can enhance the value of mixed methods research by validating findings, generating samples, and informing the development of instruments or interventions. However, the extent to which mixed methods studies implement integration remains limited. Specific approaches to integrate qualitative and quantitative research procedures and data can be implemented at the design, methods, and interpretation and reporting levels. Integration at the study design level involves three basic designs and four advanced frameworks. Exploratory sequential designs begin with qualitative data collection, followed by quantitative data collection. Explanatory sequential designs begin with quantitative data collection, followed by qualitative data collection. Convergent designs collect and analyze qualitative and quantitative data simultaneously. Advanced frameworks include multistage, intervention, case study, and participatory designs. Integration at the methods level involves connecting, building, merging, and embedding. Connecting links data through sampling. Building informs data collection approaches. Merging brings data together for analysis. Embedding links data collection and analysis at multiple points. Integration at the interpretation and reporting level involves narrative, data transformation, and joint display. Narrative integrates findings through themes. Data transformation converts data into the other type for analysis. Joint display combines data visually to draw new insights. The "fit" of integration refers to the coherence of qualitative and quantitative findings. It can result in confirmation, expansion, or discordance. Examples illustrate integration practices in exploratory sequential and convergent designs. These examples show how integration can enhance understanding of complex health issues and improve the quality of health services research. The article concludes that mixed methods research offers a new framework for health services research with potential to generate unique insights into healthcare quality, access, and delivery.