The Body Image Acceptance and Action Questionnaire (BIAAQ; Sandoz et al., 2013) is a 12-item measure of body image flexibility. Body image flexibility involves full awareness and openness to the experience of embodiment (e.g., body image thoughts, feelings, perceptions, sensations, etc.) in any one moment in such a way as to allow for engagement in valued action. The BIAAQ can be administered to adults or adolescents in person or online. This chapter discusses the development of the BIAAQ and provides evidence for its reliability and validity. More specifically, the majority of studies evaluating the psychometric properties of the BIAAQ have found the instrument to be composed of a single-factor. Internal consistency, test-retest reliability, split-half reliability, convergent validity, and incremental validity support the use of the BIAAQ. This chapter provides the BIAAQ items in their entirety, instructions for administering the scale to participants and the scoring procedure. Abbreviated and translated versions are also summarized. Logistics of use, such as permissions, copyright, and contact information, are provided for readers.