Instant messenger (IM), a communication technology originally used by individuals in their personal lives, has been increasingly adopted and used to facilitate work-related activities. Up to now, empirical research on IM use is still lacking. We conducted a qualitative study collecting interview data from a work group using IM for work purposes. We found that people have formed various patterns of IM adoption. Drawing on the theory of structure and agency, we explained that the adoption patterns are formed by both the group-level structures (peer pressure, social impact, managerial rules) and the individual-level agency factors (users’ free choice based on their technology use history, age, and use habits).