In order to plan for the professional development of English language teachers, we need to have a comprehensive understanding of what competence and expertise in language teaching consists of. What essential skills, knowledge, values, attitudes and goals do language teachers need, and how can these be acquired? This paper seeks to explore these questions by examining ten core dimensions of skill and expertise in language teaching. These are: language proficiency, content knowledge, teaching skills, contextual knowledge, language teacher identity, learner-focussed teaching, specialized cognitive skills, theorizing from practice, joining a community of practice, and professionalism. Each construct will be examined, its contribution to teacher competence and performance illustrated, and implications discussed for the development of English language teachers and teacher education programmes.