Early childhood is widely recognized as the most flexible developmental period for influencing children's future trajectories, and this critical period of development is not limited to the years before children enter formal schooling. Recognizing this, states and school districts across the country are making an effort to align the policy and practice in early care and education with subsequent K-12 systems. This issue brief provides an overview of some of the key components and challenges of pre-K to third grade, or P-3, alignment initiatives identified by implementers at the state and local levels. (see Appendix for full list of interviewees) (author abstract)