Optimising implementation strategies of the scale-up of a primary care psychological intervention: The Friendship Bench A randomised controlled trial showed unequivocally that the Friendship Bench (FB) is the first effective psychological treatment programme in primary care to be tested so far in Sub-Saharan Africa. The auspicious results persuaded the government to scale-up the FB to 72 clinics in and around Harare about one year ago. Additional scaling-up has been planned for later this year. Up until now, there has not been an evaluation of the results of this scaling-up initiative.   This study aims to evaluate the scaling-up so far but most importantly to identify the factors that have influenced the outcome of the implementation of the FB with a view to design an enhanced facilitation intervention to improve the implementation in clinics that have not performed so well. We will use two well-known implementation science frameworks (RE-AIM and CFIR) to guide our work. Whilst RE-AIM will provide us with a framework for the outcomes, CIFR will guide us through the process of exploring the 'core' factors that determine the success or failure of the implementation of the FB. We will start with an evaluation of what has been achieved so far using all the data that has been routinely collected during the scale-up effort until now. This will be supplemented with additional data captured through a survey and other qualitative methods. The results will allow us to evaluate RE-AIM outcomes and classify clinics according to their implementation outcomes. Subsequently we will conduct a workshop with the main stakeholders to discuss and agree on the CFIR framework to use for the second phase of exploration. The main aim of the second phase is to identify key or core variables deemed to be key predictors of the successful implementation of the FB. In order to do this we will focus on comparing low and high performing clinics to identify those factors that might explain implementation outcomes. During the second phase, most research will be of a qualitative nature, through focus groups and semi-structured interviews, except for small surveys and the collection of additional economic data.  At the end of this phase, we will invite main stakeholders again to review our results and conclusions and to help us identify the components of an enhanced facilitation intervention that we will test in those clinics whose implementation achievements fall into the lowest quartile. We will conduct a hybrid type 3 study to ascertain if implementation outcomes improve four months after this facilitation takes place in comparison with control clinics. The information generated in this study is vital to continue the successful expansion of the FB and to consolidate the implementation currently underway. Besides it will provide essential information for other neighbouring countries in terms of using implementation science methodology as well as learning about potential problems in the route to implementation as well as possible approaches to improve their implementation efforts. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.