Each workplace operates within a cultural context in which local features of interaction influence how employees conceptualize their workplace self. Building on small-group research, I argue that understanding these idiocultures as action arenas helps to specify how group knowledge, practices, and beliefs are expressed and affect occupational identity. To demonstrate the power of microcultures, I analyzed local offices of the National Weather Service (NWS) through ethnographic methods. I focused on the Chicago office, demonstrating how its culture, which emphasizes autonomy and resistance to authority, shapes the staff's images of scientific practice and the contours of being a scientist. The culture is revealed in their joking relations as well as in other office traditions. I then compared this culture with that of Flowerland, a spin-up office established in the 1990s. These two offices use their cultures to differentiate themselves, creating distinct work practices. As all work groups have local cultures, giving greater attention to small-group dynamics helps us understand how workers define themselves, how cultures differ, and how the effects of these differences shape the experience of work.