The Philadelphia Zoo's Measuring Mission project assessed the conservation-related impacts of a visit to the Zoo and documented the results in a way that would provide a set of easily actionable planning strategies. A logic model provided a theoretical framework and guided the development of survey items. Three groups were surveyed using a pre–post retrospective instrument: zoo visitors, members, and volunteers. This report includes findings from the visitor surveys only. Data were analyzed using factor analysis, correlations, and t-tests. Results revealed that the Philadelphia Zoo has been most successful in providing its guests with a satisfying animal viewing experience, facilitated by accessible informative interpretive staff, but that guests do not always take advantage of opportunities to interact with staff. Success in achieving the Zoo's conservation mission was measured by comparing pre and posttest scores on five outcome factors (conservation motivation, conservation knowledge, pro-conservation consumer skills, conservation attitudes/values, readiness to take conservation action). The greatest gains were found in conservation knowledge and conservation motivation. Quality of exhibits and quality of staff stand out as the most important factors in influencing conservation outcomes. To ensure that results would be accessible to a wide variety of Zoo employees for planning, program and exhibit development, and staff training, nine strategies were identified as key to achieving success in the Zoo's mission. Measuring Mission has created a process for assessing the Zoo's mission impact, and has confirmed that high-quality exhibits interpreted by expert, readily available staff can influence conservation knowledge and motivation in particular. Zoo Biol 28:473–487, 2009. © 2009 Wiley-Liss, Inc.