The book explores how the evolving global role of English as a lingua franca (ELF) challenges traditional approaches to English language teaching. Focusing on Polish in-service EFL teachers, it investigates their views and attitudes towards ELF-oriented pedagogy and outlines five key principles that form its foundation. Through a mixed-methods study conducted among English language teachers in Poland, alongside an innovative classroom project with secondary school learners, the author highlights both the benefits and challenges of implementing ELF-aware practices. Additionally, the book provides practical guidelines and sample activities to support teachers in effectively integrating ELF-oriented strategies. This work offers valuable insights for teachers and researchers seeking to adapt ELT to today's multilingual and multicultural realities, promoting a more inclusive, flexible, and context-sensitive way of teaching English in the 21st century.