The purpose of the present investigation was to examine young diplomats' socialization to the professional expert culture of the Ministry for Foreign Affairs of Finland over a six-month on-job training period, as part of their preparation for service in the diplomatic corps. Using social network analysis, we analyzed departments' internal social structures, prevailing social relations, and the young diplomats' role and position in the networks of knowledge acquisition, practical know-how, and professional collaboration. Data collected by contextual event sampling and theme interviews and analyzed by qualitative content analysis were used to characterize the young diplomats' personal social support networks, resources obtained, as well as associated reflections regarding their functioning in and socialization to the departmental workplace community. The results indicated that across the six-month training period, the young diplomats became involved to the workplace communities' networked expertise and were socialized to its expert culture, even if their achieved networking positions differed. The results revealed differences between levels of collective operational practices in the workplace communities as well as the nature of assignments in which the young diplomats participated and for which they were responsible. It was proposed that these differences mirrored distinction between expansive natures of young diplomats' workplace communities as learning environments.