This book gives an account of a recent study into the nature of teacher quality that moves beyond typical discussions of teacher impact on student results and into what it means to be a teacher. It describes how a range of different research methodologies were combined to design a process for research-informed examinations of teacher quality and the predictive validity of teaching performance assessments.The authors present qualitative and quantitative evidence that reveals how education stakeholders including teachers perceive what teacher quality is and what it might look like in the classroom.They aim to shift the discourse on this issue by changing the language we use to talk about teachers and what they do.In re-examining how we think about teachers, this work highlights the complex nature of defining teacher quality and what is required for successful engagement in the profession. Putting forth a new understanding of teacher quality, this is an essential resource for education academics and students, as well as teaching professionals.Further information about the study discussed in this book is available at https://www.sydney.edu.au/arts/our-research/research-projects/teacher-quality/whats-the-evidence.html.