This chapter presents definitions that reflect the terminology used in the most frequently cited manuscripts and reports on dissemination and implementation (D&I) research in health and in funding announcements of major federal funding agencies. The chapter is organized as follows. The first section provides definition for the most commonly used terms in D&I research. The second section identifies stages of the research process continuum and their relationship to D&I -related activities and defines varieties of Type 1 and 2 research. In the third section, the most commonly used models and frameworks that can inform planning and evaluation activities in D&I research are discussed. The fourth section defines key factors that are related to the success, speed, and extent of D&I. Finally, the fifth section summarizes important concepts of study design and measurement that should be considered when evaluating D&I research.