The purpose of this study was to develop a theoretically-driven instrument of achievement motivation and determine its validation. The Achievement Motivation Measure (AMM) is closely aligned with Atkinson and McClelland's (1948, 1953, 1961) theoretical constructs of achievement thoughts and behaviours. Confirmatory and exploratory factor analysis (CFA and EFA) methods evaluated the structural validity of a newly developed instrument, the AMM, by assessing achievement thoughts and behaviours. Participants included 632 graduate and undergraduate university students. EFA supported two factors (Achievement Thoughts and Achievement Behaviours) with 13 items. Findings of a CFA supported the modified two-factor model as fitting the data. The theoretically supported AMM effectively measured achievement motivation by assessing achievement thoughts and behaviours.