The APA Division 16 Working Group on Translating Science to Practice contends that implementation science is essential to the process of translating evidence-based interventions (EBIs) into the unique context of the schools, and that increasing attention to implementation will lead to the improvement of school psychological services and school learning environments. Key elements of implementation and implementation science are described. Four critical issues for implementation science in school psychology are presented: barriers to implementation, improving intervention fidelity and identifying core intervention components, implementation with diverse client populations, and implementation in diverse settings. What is known and what researchers need to investigate for each set of issues is addressed. A discussion of implementation science methods and measures is included. Finally, implications for research, training and practice are presented.