Supporting high quality teaching is pivotal in improving children's outcomes. Indeed, research tells us that high quality teaching can narrow the disadvantage gap. It is therefore hugely encouraging to see a host of new initiatives and reforms that recognise the importance of teacher quality such as the Early Career Framework and the new National Professional Qualifications. These exemplify a growing consensus that promoting effective professional development (PD) plays a crucial role in improving classroom practice and pupil outcomes, and this guidance further reflects this, offering recommendations on how to improve professional development and design and select more impactful PD. PD has great potential; but it also comes with costs. We know that teachers engage in professional development activities whilst balancing multiple and, at times, competing commitments and time pressures. The need is clear, therefore, for PD to be well-designed, selected, and implemented so that the investment is justified. This guidance will support schools in selecting external PD and designing and delivering their own PD. It will also support external providers in designing, delivering, and explaining their offering to schools. To develop the report's three recommendations, the authors reviewed the best available international research as well as current practice, and consulted with school leaders and academics. As with all Education Endowment Foundation (EEF) guidance reports, its publication is just the start of how the authors aim to support schools in implementing these recommendations. The authors will be working with the sector, including through colleagues in the Research Schools Network, to build on them with further training, resources and tools. [For the report, "What Are the Characteristics of Effective Teacher Professional Development? A Systematic Review and Meta-Analysis," see ED615914.]