Micro-credentials (MCs) are a rapidly expanding element of modern teacher professional learning. In this brief, we provide a concise review of what is currently known about MCs: how they work, their strengths, their shortcomings, and what we still need to learn. For districts and states that are considering introducing MCs, this brief is designed to ground implementation efforts in emerging best practices. This brief is intended for both educators and researchers to improve and support teacher professional learning. The document includes a forward looking research agenda focused on the MC practices that are most likely to result in positive outcomes for teachers and students. [Contributing authors to this brief include Jessie Kerr-Vanderslice, Jason LaTurner, and Liz Nelson.]