Approximately 200,000 anterior cruciate ligament (ACL) injuries occur each year with about 100,000 of these injuries undergoing reconstruction (ACLR). The impetus of ACLR is to allow previously high functioning, physically active individuals to return to desired levels of sports participation and to engage in recommended levels of physical activity. However, 1 out of 3 patients after ACLR fail to return to competitive levels of sport and meet recommended levels of physical activity. Injury-related fear has been cited as the primary barrier for failure to return to sport. However, the research has been primarily qualitative in nature and limited research has quantitatively examined the impact of injury-related fear on return to sport and physical activity engagement in this population. In addition to quantifying the impact of injury-related fear, no research has examined the underlying neural substrates associated with injury-related fear after ACLR. Previous research has demonstrated that patients after ACLR undergo neuroplasticity in sensorimotor regions of the brain and exhibit changes in neurocognitive functioning. Despite previous research in other musculoskeletal pathologies demonstrating neuroplasticity in emotional regulation centers of the brain, no research has examined these brain regions in patients after ACLR. Furthermore, previous research in healthy athletes has suggested that psychosocial impairments can lead to changes in neurocognitive functioning, including reaction time. Understanding these neural substrates could provide insight into appropriate intervention strategies to decrease injury-related fear, increase return to sport and physical activity engagement, and potentially improve neurocognitive functioning in patients after ACLR. The purpose of this dissertation was to further investigate the effects of injury-related fear on patients after ACLR and to determine the efficacy of a cognitive behavioral intervention to decrease injury-related fear in this population. The purposes of these studies were to determine whether patient-based, specifically psychological, and functional outcomes were associated with return to sport and physical activity levels in individuals with a history of ACLR, to determine differences in brain activation patterns when exposed to fear-eliciting stimuli in individuals with a history of ACLR compared healthy matched controls, and to determine the efficacy of in vivo exposure therapy on self-reported fear and reaction times in participants post-ACLR. The results of these studies indicate that injury-related fear was quantitatively associated with return to sport and physical activity engagement in patients after ACLR. Additionally, individuals with a history of ACLR activated emotional regulation centers of the brain in greater depth when compared to healthy matched controls. Lastly, in vivo exposure therapy decreased self-reported injury-related fear for specific functional tasks but did not improve general fear response or reaction time in post-ACLR participants. The results of these studies objectively elucidate the negative impact of injury-related fear in patients with a history of ACLR.