1Impairment-based evaluation has, until recently, been the mainstay of orthopaedic 2 research in anterior cruciate ligament (ACL) reconstruction. However, participation-3 based outcomes, in particular returning to sport, have lately garnered increased 4 research attention. This is important because returning to sport is typically a main 5 concern of injured athletes. Recent meta-analyses have demonstrated that the return to 6 sport rate after ACL reconstruction is disappointingly low, and that a range of 7 contextual factors including age, sex, sport participation level and psychological 8 factors may affect the return to sport rate. Moderate to large effect sizes have been 9 demonstrated for greater psychological readiness to return to sport, and lower fear of 10 re-injury favouring returning to the pre-injury level sport after ACL reconstruction. 11Understanding the relationship between psychological factors and returning to sport is 12 essential in light of the fact that most athletes recover good physical function after 13 surgery, and many athletes with good knee function do not return to sport. 14 Psychological factors are potentially modifiable with appropriate intervention, yet 15 these factors are not systematically addressed in routine post-operative rehabilitation. 16This review summarises the recent evidence for the relationship between 17 psychological factors and ACL injury, including recovery from injury and returning 18 to sport. 19 3