Many instruments recommended for measuring attitudes toward fatness and “obesity” were developed in the 1990s, a time when the “obesity epidemic” was gaining momentum and anti-fat rhetoric was normative. Consequently, these instruments have tended to focus on assessing negative appraisals of fatness and fat people and reinforce weight stigma. As fat discourse has matured and expanded to incorporate fat positive attitudes, a nonstigmatizing way of measuring contemporary fat attitudes and beliefs in quantitative research is required. To address this need, we developed the Fat Attitudes Assessment Toolkit (FAAT). In this article, we describe the development of the FAAT and provide initial evidence for the scale’s validity and psychometric properties across three studies. Study 1 included a systematic process for developing the extensive item pool that was reviewed by subject matter experts and a community panel. We explored and identified an initial multidimensional structure for the FAAT. Study 2 expanded and confirmed the factor structure with additional analyses in an independent sample and provided evidence for the overall reliability of the subscale scores and reliability as a function of gender and identification as fat. Construct and criterion validity of the subscale scores were also demonstrated. Study 3 provided evidence for the test-retest reliability of the FAAT subscales scores over time. The FAAT includes nine robust scales: Empathy, Activism Orientation, Size Acceptance, Attractiveness, Critical Health, General Complexity, Socioeconomic Complexity, Responsibility, and Body Acceptance. Specific subscales can be combined to form two composite measures: Fat Acceptance and Attribution Complexity. The scales that comprise the FAAT measure specific elements of attitudes towards fat people that are frequently targeted in weight stigma reduction research and activism; the FAAT thus offers a powerful and precise method for evaluating weight stigma reduction interventions that allows for an assessment of shifts toward more positive attitudes.