In the present study the construct inquiry of mind explored and an instrument to measure it is proposed. Using three different samples, explorative and confirmative factor analyses were performed, resulting in three empirical dimensions that correspond to the three theoretical dimensions: 1) 'value deep understanding,' 2) 'reserve judgment and tolerate ambiguity,' and 3) 'taking a range of perspectives and posing increasingly focused questions.' Our findings suggest the teachers' inquiry habit of mind scale has good psychometric properties making it useful not only for research that investigates teachers' research attitude and intention to do research but also as an evaluation tool for the development of an inquiry habit of mind in both student teachers and teacher educators (in teacher education) as well as in experienced teachers (participating in professional development).