Research on the transition to kindergarten in the United States of America [USA] during the first quarter of the twenty-first century has been largely influenced by an ecological model that emphasizes the interrelated influence of relationships among children, families, schools, peers, and neighborhood contexts. This same time period has also been one of consequential shifts in the policy landscape of both pre-kindergarten and K-12 education in the USA. To illuminate how research, policy, and practice intersect, this chapter examines peer-reviewed literature about transitions to kindergarten in the USA to identify how policy- and practice-relevant strategies have been examined. It critiques the prevalent theoretical framing of the transition to kindergarten in the USA from 2000 to 2024, and identifies continuities and discontinuities in how research has investigated (or not) its multiple facets. It highlights practical implications from the literature and offers future directions for the next 25 years of research, policy, and practice for transitions to kindergarten in the USA.