The use of videos to inform teacher-practice has been common in research and in pre-service teacher education for many years. However, more recent interest has focused on how videos may be used for professional development of teachers, as separate from the more common research focus. A Discussion group entitled 'Videos in Teacher Professional Development' at ICME-13 in Hamburg (International Congress on Mathematical Education, 24-3` July 2016) showcased a number of initiatives from across the world, including Australia, New Zealand, Singapore and the USA. This chapter will briefly summarize the wider discussions and then consider in more depth the findings and implications from one of the projects presented in the forum. This project investigated the largely unexplored area of professional development for undergraduate mathematics lecturers, working in collaboration with mathematics educators in a university mathematics department (Barton et al., 2015). Here we present key findings from this longitudinal project at the University of Auckland, New Zealand. which developed a model for professional development, theoretically grounded in Schoenfeld's (2010) resources, orientations and goals (ROG) model of teacher action. As part of this project, a group of around 6-8 lecturers have been meeting regularly since 2010 to discuss and analyze video excerpts of their lecturing, along with written pre- and post-lecture statements of their "ROGs". Along with (as expected) evidence of improved teaching performance, we also identified important aspects of our practice and of undergraduate mathematics that received repeated attention. The discussions often tended to focus on mathematical and epistemological aspects of the lectures and provided informative insights into lecturer behaviour in mathematics, and the theoretical lens through which this was being framed. The trial has been successful enough to be expanded into further groups that now constitute a professional development culture at Auckland. and has recently been adopted by several other universities, including groups at Monash and the University of Melbourne, Australia. The chapter will consider the elements of the project that are considered essential for its ongoing success, highlight the project's significance and implications for ongoing professional development in undergraduate mathematics, and consider its potential for further informing our theoretical perspectives in mathematics education with respect to both mathematical epistemology and teacher knowledge and practice.