The papers in this collection, drawn from the 34th Annual Conference of the British Association for Applied Lunguistics, reflect a number of different perspecitves within the field of applied linguistics at the start of the twenty-first century. While addressing the theme of unity and diversity, each paper prompts critical reflection on tensions within the descipline between stability and change, consensus and controversy, similiarity and variation. The interpretation of languge use is broad and varied, taking both macro- and micro-perspectives. Topics address range from issues of global communication in a world of shifting demographics and technological advances to analyses of specific contexts of interaction, both professional and personal. Contexts of language use frequently coincide with settings of language acquisition, both within and beyond the language classroom, and this opens up discussion of the focus, scope and appropriateness of research stances in applied linguistics and practices in language pedagogy.Furthermore, variation is considered from a number of social-cultural, gender-related, linguistic and discourse perspectives, calling into question terminology, definitions and the nature of evidence at the heart of applied linguistics theory and practice. Kristyan Spelman Miller is a lecturer in Applied Linguistics in the School of Linguistics and Applied Language Studies at the University of Reading. Paul Thompson is a Research Fellow in the School of Linguistics and Applied Language Studies at the University of Reading.