This article describes the development, implementation, and evaluation of an online course designed to train early interventionists to implement strategies with caregivers (parents) that promote interactions with infants who have multiple disabilities. The focus was on supporting caregivers to observe and understand their infants' states and cues, and to develop responsive interaction strategies that encourage their infants' development of intentional communicative behavior. Because infants with multiple disabilities represent a low-incidence and challenging population, there is a significant need for efficient inservice methods, such as online instruction. A total of 86 early interventionists in California completed the online course successfully and used the strategies effectively with caregivers and their infants. An overview of the course content, structure, assignments, and online instruction is provided. A discussion of outcomes includes feedback from students on (a) their perception of changes in their own professional competencies based on pre- and posttest data, (b) their satisfaction with the overall course design, (c) challenges and benefits of online instruction, and (d) the impact of what they learned on their professional practice. Course effectiveness was also measured through informal analyses of online discussions, course assignments, and instructor reflections. Implications for future professional development efforts are identified.