This paper describes the application of mixed method designs in implementation research across 22 mental health services research studies published in peer-reviewed journals over the last five years. The study identified seven structural arrangements of qualitative and quantitative methods, five functions of mixed methods, and three ways of linking quantitative and qualitative data. Complexity of design was associated with the number of aims or objectives, study context, and phase of implementation examined. The findings provide suggestions for the use of mixed method designs in implementation research. Mixed methods designs combine qualitative and quantitative data to provide a better understanding of research issues than either approach alone. Qualitative methods explore reasons for success or failure in implementing evidence-based practices (EBPs), while quantitative methods test hypotheses based on existing models. The study found that 9 of the 22 studies used quantitative and qualitative methods sequentially, while 19 used them simultaneously. Six studies used both sequential and simultaneous approaches. The weighting of methods varied, with 19 studies using quantitative methods as primary and qualitative as secondary. Ten studies used balanced designs with equal weighting of both methods. The study identified five functions of mixed methods: convergence, complementarity, expansion, development, and sampling. Convergence involved using both methods to answer the same question, while complementarity involved using them to answer related questions. Expansion used qualitative data to explain quantitative findings. Development involved using qualitative data to develop new measures or interventions. Sampling involved using one method to identify participants for the other. The study also examined the use of mixed methods in different phases of implementation, including exploration, adoption, implementation, and sustainability. The findings suggest that mixed methods are useful for understanding the context of implementation, measuring intervention outcomes, and incorporating the perspectives of stakeholders. The study highlights the importance of using mixed methods to understand the complex nature of implementation research and to improve the effectiveness of evidence-based practices in mental health services.This paper describes the application of mixed method designs in implementation research across 22 mental health services research studies published in peer-reviewed journals over the last five years. The study identified seven structural arrangements of qualitative and quantitative methods, five functions of mixed methods, and three ways of linking quantitative and qualitative data. Complexity of design was associated with the number of aims or objectives, study context, and phase of implementation examined. The findings provide suggestions for the use of mixed method designs in implementation research. Mixed methods designs combine qualitative and quantitative data to provide a better understanding of research issues than either approach alone. Qualitative methods explore reasons for success or failure in implementing evidence-based practices (EBPs), while quantitative methods test hypotheses based on existing models. The study found that 9 of the 22 studies used quantitative and qualitative methods sequentially, while 19 used them simultaneously. Six studies used both sequential and simultaneous approaches. The weighting of methods varied, with 19 studies using quantitative methods as primary and qualitative as secondary. Ten studies used balanced designs with equal weighting of both methods. The study identified five functions of mixed methods: convergence, complementarity, expansion, development, and sampling. Convergence involved using both methods to answer the same question, while complementarity involved using them to answer related questions. Expansion used qualitative data to explain quantitative findings. Development involved using qualitative data to develop new measures or interventions. Sampling involved using one method to identify participants for the other. The study also examined the use of mixed methods in different phases of implementation, including exploration, adoption, implementation, and sustainability. The findings suggest that mixed methods are useful for understanding the context of implementation, measuring intervention outcomes, and incorporating the perspectives of stakeholders. The study highlights the importance of using mixed methods to understand the complex nature of implementation research and to improve the effectiveness of evidence-based practices in mental health services.