On 24th and 25th September 2019 Cardiff University and Cynnal Cymru hosted the Sustainable Built Environment Conference: SBE19Wales Policy to Practice, at the Principality Stadium, Cardiff. The aim of SBE19Wales Policy to Practice was to bring together climate and energy researchers, built environment professionals, policy experts and government officials to focus on the transition of energy and low carbon policies into practice. The conference topics allowed delegates to increase their knowledge and skills related to climate change policies and actions, building design and retrofit issues and the performance of buildings and materials. The papers have been grouped according to themes. The International Sustainable Built Environment Conference Series began in 2000 and operates on a three year cycle starting with a year of planning, followed by a year of national or regional conferences, culminating in a single global event in year three. The series places a core emphasis on peer-reviewed papers, presentations of regional policy papers, displays of pre-evaluated projects and a small number of high-quality commercial exhibits. These events also provide fast-track inclusion of the best technical papers from national/regional conferences into the global event, as well as registration policies designed to encourage the attendance of students and delegates from developing countries. In all of these conferences, one or more local research-based organisations take on the financial and organizational responsibility while the international series owners, CIB, iiSBE, FIDIC and UN Environment provide organisational advice and use their networks to ensure a large multi-disciplinary audience for the events.