In an increasingly fast-changing and diverse world, the importance of developing social and emotional skills is becoming more evident. The large body of accumulated evidence shows that these skills have strong relationships with life outcomes and they have been referred to as a key component of 21st century skills. The Organisation for Economic Co-operation and Development (OECD) Study on Social and Emotional Skills is a new international assessment of these skills in students at primary and secondary schools. This study also gathers information on students’ families, schools and community learning contexts, aiming to provide information about the conditions or practices that foster or hinder the development of these critical skills. This paper will examine the development of the study – based on the ‘Big Five’ model of personality characteristics – and describe developments so far.