States have often introduced programs supporting science, technology, engineering and math in the secondary grades. Yet the evidence of STEM's positive impact on young children's development makes a compelling case for engaging learners in pre-K through third grade in consistent, authentic and high-quality STEM experiences. High-quality P-3 STEM learning need not -- and should not -- be viewed as an add-on to an already crowded set of learning objectives. Instead, states can integrate early STEM opportunities to advance developmentally appropriate practice and young learners' growth in literacy and numeracy, executive function and 21st century skills. This Policy Guide, informed by experts in early education and STEM fields, identifies policies and actions a state can adopt to bring STEM opportunities to the early grades.