Background <p>The demand for implementation science training far exceeds supply, indicating a need to expand capacity building efforts. Since 2014, the Implementation Science Summer Institute at the University of Washington (ISSI-UW) has provided an annual intensive training program to strengthen capacity in implementation science. In this article, we describe an evaluation of the program to determine its impact on short and long-term outcomes.</p> Methods <p>We used the Kirkpatrick model to guide the evaluation. We administered pre- and post-surveys with 2024 trainees to evaluate changes in implementation science knowledge and skills, intent to use methods and tools, and overall satisfaction. A survey of alumni from 2014 to 2024 evaluated post-training engagement in implementation science-related activities, the course’s impact on alumni work, and its effect on professional networks. Surveys included both closed- and open-ended questions. Descriptive statistics were used to analyze demographic characteristics and present Likert-type response frequencies. Wilcoxon rank-sum tests were used to compare median differences across surveys and to determine statistical significance. Qualitative content analysis was conducted to examine open-ended responses.</p> Results <p>Of the 477 individuals from 48 countries (69% were low and middle-income countries) trained at the institute between 2014 and 2024 who were invited to participate in the alumni survey, 136 (28%) responded. Of the 72 individuals invited to participate in the 2024 pre- and post-surveys, 54 (75%) and 51 (70%) responded, respectively. Participants included global health researchers, implementers, graduate students, and donors. Findings from the 2024 pre- and post-surveys showed a significant improvement in the median responses for knowledge, skills, and intent, and respondents expressed high satisfaction. Alumni reported incorporating skills related to implementation science theories, models, and frameworks (84%), design of implementation evaluations (52%), and writing grants (50%) into their work. Alumni reported that the course had a very large (21%) or large influence on their work (32%) and noted a positive impact on networking (66%).</p> Conclusions <p>The ISSI-UW was associated with short-term improvements in implementation science knowledge and longer-term integration of implementation science methods and tools in professional work. This is an example of how universities can contribute to expanding and building capacity in implementation research and practice.</p>