The present study was carried out to develop and validate an L2 teacher reflection instrument. For this purpose, a six component model of second language (L2) teacher reflection, encompassing practical, cognitive, meta-cognitive, affective, critical and moral reflection, was developed using experts' opinion and a comprehensive review of the related literature. This initial model was then operationalized in an instrument consisting of 42 items, i.e. 7 behavioral items for each component. The piloting and testing of the tentative model through exploratory and confirmatory data analyses on a sample of 300 ESL teachers reduced the instrument to 29 items, removing the "morality" factor, and reducing the items in the "affective" factor to half. (Contains 3 figures and 4 tables.)