Behavior—what a person does to attain a goal—relevant to temporomandibular disorders (TMDs) can be classified into three types: organ system-level functional behaviors, organ system-level non-functional behaviors, and person-level behaviors. Despite decades of productive research regarding the importance of behavior, taken broadly, as encompassing multiple risk factors for another prevalent musculoskeletal pain disorder (low back pain), behavioral research related to TMDs remains in the early stages. Clinically, behavioral factors are complex with regard to adequate assessment, and they require specific conceptual and management skills. Consequently, providing due diligence to their importance is challenging in many medical arenas. The sparse data that exist supporting the role of behavior in TMD onset and persistence indicate that excessive extent of masticatory system non-functional and possibly functional behaviors contributes to painful TMD onset and appear to contribute to chronicity. In addition, TMD-relevant behaviors can be amplified by chronic pain, among other stressors, suggesting a complex reciprocal relationship. Both the reciprocal relationship between TMD pain and functional and non-functional behaviors and the person-level behaviors create multiple interactive feedback loops which then serve as barriers to behavioral change. These barriers need to be addressed in a step-like manner with treatment, such that motor control and sensory perception undergo re-learning. At present, the evidence regarding treatments or their efficacy is minimal and mostly indirect. The field needs to develop better theories regarding how behavior fits within the available evidence pertaining to TMD etiology and persistence. With better theories and transfer of knowledge from other pain fields, better treatment research can be implemented for TMDs.