Abstract. As a response to the lack of quantitative and reliable measures of the team adaptation process, the aim of the present study was to develop and validate an instrument for assessing the four phases of the team adaptation process as described by Rosen and colleagues (2011) . Two trained raters and two subject matter expert groups contributed to the development of four behaviorally anchored rating scales (BARS) that span across the spectrum of team processes involved in each team adaptation phase. To validate the four BARS, two different trained raters assessed independently the team adaptation phases of 66 four-person teams. The validation study provided empirical support for the BARS’ psychometric adequacy. The BARS measures overcame the common middle anchor problem, showed sensitivity in differentiating between teams and between the four phases, showed evidence for acceptable reliability, construct, and criterion validity, and supported the theoretical team adaptation process assumptions. The study contributes to research and praxis by enabling the direct assessment of the overall team adaptation process, thereby facilitating our understanding of this complex phenomenon. This allows the identification of behavioral strengths and weaknesses for targeted team development and comprehensive team adaptation studies.