Instruction in prekindergarten through third grade (P-3) lends itself to authentic, project-based and playful experiences that immerse learners in STEM activities and instruction. In an era of increased focus on literacy and math skills, STEM provides an interdisciplinary approach that may prove more effective for young students to acquire skills across several subject areas. P-3 teachers need specific training to understand what comprises high-quality early STEM learning experiences and to be equipped to offer learners these experiences on a consistent basis. However, the experiences of most P-3 educators do not prepare them to provide integrated STEM instruction, as demonstrated by the limited requirements for pre-service and in-service elementary teachers in STEM subjects. This Policy Brief explores the critical components for early STEM training and professional development for teachers, which includes acknowledging and overcoming math anxiety and implementing teacher training in tandem with other supports, such as principal training and high-quality curricular resources. This brief also provides examples of the types of approaches state policymakers use to create a policy environment that supports implementation of these components. This includes statewide approaches, those that blend in regional approaches and innovations in designing training content. Lastly, policy considerations are provided to build out a comprehensive approach.