This is a book for practitioners, university educators, workplace learning educators, researchers and the professions. It draws together two key elements of the lives of these people: professional practice – what people do, and practice discourse – what they write and say about what they do. And, it focuses these discussions around two spaces – the core and the margins, of practice and discourse. Writing in the margins of texts has a very long history. People have always left part of themselves – their ideas, personality and reflections – in the margins of texts. In this book we have taken up the idea of such written marginalia and we have expanded it into writing into the texts of practice discourse as well as speaking and acting in the margins of professional practice. Such deliberate practice changes in marginal practice spaces and in written practice discourse provides ways of shaping and critically appraising current and future professional practice. This book provides a dialogue between two fascinating phenomena: professional practice and discourse. In the 21st century these two are facing challenges as they negotiate their contested spaces in a rapidly changing global society. They draw on strong established traditions and expectations but they cannot be complacent in these illusory stabilities. Rather they must be awake to the imperatives of their own re-invention and re-claimed relevance to today’s society and today’s professional class in the workforce. Across the chapters we explore the core spaces of professional practice discourse from the vantage point of the margins of this space, and the margin spaces as they interact with the core. Marginalia serves as an architect of destabilisation, challenge, revolution, reflection or sometimes affirmation of the central discourse space. There are five sections in the book: Section One: Professional practice discourse, Section Two: Leading the practice discourse, Section Three: Writing from inside practice, Section Four: Writing onto and into practice and Section Five: Marking trails and stimulating insights. Readers are invited to contribute to our exploration of the phenomenon and practice of professional practice discourse marginalia.