639/Administrative Science Quarterly, 55 (2010): 639–670 © 2010 by Johnson Graduate School, Cornell University. 0001-8392/10/5504-0639/$3.00. • We thank Filip Agneessens, Dan Brass, Deborah Gibbons, Dan Halgin, Martin Kilduff, Joe Labianca, Jos van Ommeren, Anita Prasad, Wouter Stam, Christian Troester, participants of the third ION conference, and participants of the INSEAD Conference on Network Evolution for their helpful suggestions on previous versions of this manuscript. The first author is especially grateful to Mike Newman and Edu Spoor for their invaluable guidance and support during the initial stages of this research. Our paper benefited enormously from feedback we received from our editor, Phil Anderson, and the three anonymous reviewers. We thank Linda Johanson for her thoughtful feedback and expert copy-editing. This research was funded in part by a grant awarded to the first author by the Information Systems department, VU University Amsterdam, and a grant co-awarded to the second and third authors by the U.S. Defense Threat Reduction Agency. Network Churn: The Effects of Self- Monitoring Personality on Brokerage Dynamics Zuzana Sasovova VU University Amsterdam Ajay Mehra University of Kentucky Stephen P. Borgatti University of Kentucky Michaéla C. Schippers Erasmus University Rotterdam The apparent stability of social network structures may mask considerable change and adjustment in the ties that make up the structures. In this study, we theorize and test—using longitudinal data on friendship relations from a radiology department located in the Netherlands—the idea that the characteristics of this “network churn” and the resultant brokerage dynamics are traceable to indi- vidual differences in self-monitoring personality. High self-monitors were more likely than low self-monitors to attract new friends and to occupy new bridging positions over time. In comparison to low self-monitors, the new friends that high self-monitors attracted tended to be relative strangers, in the sense that they were uncon- nected with previous friends, came from different func- tions, and more efficiently increased the number of structural holes in the resultant network. Our study suggests that dispositional forces help shape the dynamic structuring of networks: individuals help (re)create the social network structures they inhabit. • Organizations are, among other things, social arenas in which people form, change, and dissolve relationships with their colleagues. We know that the structure of these relationships considered at a given point in time matters. In particular, there is considerable evidence that individuals who occupy broker- age positions bridging the “structural holes” between discon- nected others in the workplace receive higher performance evaluations and faster promotions (e.g., Burt, 1992, 2005, 2010). While it is no doubt useful to know that certain net- work structures can be advantageous, a theory that accounts for the appearance, transformation, and disappearance of network structures may provide us with a better understand- ing of the mechanisms responsible for observed network effects (Emirbayer and Goodwin, 1994) and a richer apprecia- tion for how collective action is organized (Salancik, 1995). Research has tended to treat social networks as relatively static (e.g., Moreno, 1953; cf. Nadel, 1957: 125–152). But there is growing recognition that networks are in fact dynamic systems (e.g., Weesie and Flap, 1990; Barabasi and Albert, 1999; see Doreian et al., 1996; Newman, Barabasi, and Watts, 2006). Certain global characteristics of a network (such as its overall connectivity) can appear to be stable, but this apparent stability may mask ongoing change and adjustment in the ties that constitute the network. A recent reanalysis of a classic study of friendship networks (Newcomb, 1961) found that whereas earlier studies had concluded that the network had quickly stabilized, there was in fact considerable evidence of change at the level of individual ties throughout the observation period (Moody, McFarland, and Bender- deMoll, 2005). The origins of these network dynamics are important to understand because they could help explain how network structures appear to retain their stability even as the ties they are composed of are changing. Over time, brokers may try to create new bridging relations with new people, keep apart the people they have been bridging, or attempt to bring together the people they previously bridged. Although structural holes theory makes