Although there are effective evidence-based interventions (EBIs) to prevent, treat and coordinate care for chronic conditions they may not be adopted widely and when adopted, implementation challenges can limit their impact.  Implementation strategies are “methods or techniques used to enhance the adoption, implementation, and sustainment of a clinical program or practice”. There is some evidence to suggest that to be more effective,  strategies should betailored; that is, selected and designed to address specific determinants which may influence implementation in a given context.Despite the growing popularity of tailoring the concept is ill-defined, and the way in which tailoring is applied can vary across studies or lack detail when reported. There has been less focus on the part of tailoring where stakeholders prioritise determinants and select strategies, and the way in which theory, evidence and stakeholders’ perspectives should be combined to make decisions during the process. Typically, tailoring is evaluated based on the effectiveness of the tailoredstrategy, we do not have a clear sense of the mechanisms through which tailoring works, or how to measure the “success” of the tailoring process. We lack an understanding of how stakeholders can be involved effectively in tailoring and the influence of different approaches on the outcome of tailoring.Our research programme, CUSTOMISE (Comparing and Understanding Tailoring Methods for Implementation Strategies in healthcare) will address some of these outstanding questions and generate evidence on  the feasibility, acceptability, and efficiency of different tailoring approaches, and build capacity in implementation science in Ireland, developing and delivering training and supports for, and network of, researchers and implementation practitioners. The evidence generated across the studies conducted as part of CUSTOMISE will bring greater clarity, consistency, coherence, and transparency to tailoring, a key process in implementation science.