Due to data limitations, very little is known about patterns of cross-state teacher mobility. It is an important issue because barriers to cross-state mobility create labor market frictions that could lead both current and prospective teachers to opt out of the teaching profession. In this paper, we match state-level administrative data sets from Oregon and Washington and present evidence on patterns of in-service teacher mobility between these two states. We find levels of cross-state mobility that are drastically lower than levels of within-state mobility, even when accounting for proximity to the border. These findings are consistent with the hypothesis that there are significant penalties to cross-state mobility that may be attributable to state-specific licensure regulations, seniority rules and pension structures. [This paper was published in "Educational Researcher" v44 n8 p421-431 2015 (EJ1082062).]