The evolution of the genetic counselor profession is rapidly expanding for several reasons, including the increasing number of genetic tests, the low number of medical geneticists and the increasing number of medical services. Although there have been several studies showing the efficacy of genetic counseling interventions (McAllister & Dearing, 2016), understanding why genetic counseling works, for whom and under which conditions is an area less investigated. With this project, our main aim is to develop and implement an assessment methodology to investigate the predictors of outcome in genetic counseling. The first three studies are aimed at the identification of genetic counseling core competences and predictors of efficacy: (1) what makes genetic counselling work; (2) what core competences are essential for genetic counselling; (3) what is the relationship between genetic counsellors’ competences and the efficacy of genetic counselling process; (4) which of the genetic counselors’ characteristics contribute most to the genetic counseling outcome; (5) what constitutes effective genetic counseling. The fourth study is focused on developing and implementing an instrument aimed at assessing genetic counselors’ core competences in international settings: similarities and differences in genetic counselling practice in terms of personal or professional characteristics in various international settings.