This edited collection contains sixteen papers presented at the 12th METU International ELT Convention, “Celebrating Diversity”, held in 2015 in Ankara, Turkey. With the social, cultural and technological changes the 21st century has brought to our lives, every learner today has more diverse needs and expectations, which makes us consider the concept of “diversity” as one of the core points in English language education. Based on the core principle “One size does not fit all”, this volume presents a wide range of topics and covers issues related to diversity in student and teacher profiles, teaching and learning practices, assessment techniques, world Englishes and cultural elements in EFL/ESL classrooms. As such, the proceedings of the 12th METU International ELT Convention are an invaluable reference for those interested in diverse perspectives, applications and practices in the teaching of English as a foreign and second language.