The CASEL Collaborating States Initiative (CSI) observed that state policymakers who have created foundational policies to advance social and emotional learning (SEL) often become interested, as a next step, in creating a statewide community of practice (CoP) to engage districts and schools around a shared vision to promote implementation of SEL. This playbook was developed in collaboration with state policy teams participating in the CSI over the past five years. It includes lessons learned from CSI CoPs that have advanced SEL at the state level (with 42 states), integrating SEL into MTSS (9 states), and integrating SEL into career and workforce development (12 states). In addition, this playbook is informed by the work of CASEL's Collaborating Districts Initiative (CDI) which has worked with 20 partnering districts over the past 10 years. It is designed specifically to support state teams as they work to build and sustain an effective within-state CoP centered on SEL. The playbook offers simple, user-friendly guidance that identifies key principles, processes, tools, and resources which can be utilized to organize, launch, and implement a statewide CoP designed to promote SEL.