This chapter focuses on teacher professionalism. In response to vigorous debates initiated in the disciplines of education and sociology, this issue has been discussed with varying degrees of intensity in the field of English language teaching over the past three decades. The concept of teacher professionalism, however, has an intricate nature. Its complexity partially results from the fact that it cannot be fully explained without linking it to teachers’ professional knowledge, practice, and engagement, teachers’ professional identity, and their ethical conduct, all of which are sophisticated constructs in their own right. The complexity of teacher professionalism is also attributed to its evolution within active and learning communities of English language teachers. With this in mind, this chapter begins with a presentation of important definitions of teacher professionalism. This is supported by a brief examination of the professional standards obligatory for the teaching occupation. These are discussed in relation to three dimensions: professional knowledge, professional practice, and professional engagement. The chapter then explicates the construct of teacher professional identity. This is followed by a concise deliberation on the relationship between professionalism and ethics. The chapter concludes with constructive suggestions for sustaining teacher professionalism.