The anterior cruciate ligament (ACL) serves to stabilise the knee complex and prevent intraarticular knee structures from sustaining damage during multiaxial, high impact movement. An ACL rupture most commonly occurs in adolescents and young adults taking part in competitive sports and causes substantial disruption to the knee joint. Anterior cruciate ligament reconstruction (ACLR) is the most common treatment offered to ACL-ruptured individuals worldwide. Individuals undergoing this surgery often have high expectations that rarely match surgical outcomes. Return to sport rates are low, re-injury fears are widespread and many individuals develop knee osteoarthritis within ten years of ACLR. This mismatch between expectations and actual outcomes has great potential to impact longer-term quality of life (QOL). The primary aims of this thesis were to: (i) generate a detailed picture of longer-term QOL following ACLR, and (ii) identify factors related to longer-term QOL in people with knee pain, symptoms or functional limitations following ACLR.The first study in this thesis is a systematic review that revealed impaired knee-related QOL at 5 to 20 years after ACLR. However, it became evident that research into factors impacting upon QOL in this population was scarce. The systematic review found that having a subsequent knee injury, an additional knee surgery after ACLR, and developing severe radiographic osteoarthritis were associated with worse QOL outcomes. The second study in this thesis is a systematic review that investigated QOL more than five years after ACL rupture in individuals who remained ACL-deficient (did not undergo ACLR) and compared QOL between ACLdeficient and ACL-reconstructed groups. This systematic review found that ACL-deficient individuals reported comparable QOL outcomes to those who underwent ACLR 5 to 25 years previously. All studies that reported QOL after ACLR included asymptomatic participants without knee difficulties, which may underestimate the degree of QOL impairment experienced by people with ongoing knee difficulties.The third study in this thesis used a cross-sectional design to describe QOL outcomes in 162 individuals with knee pain, symptoms or functional limitations 5 to 20 years following ACLR.It showed that individuals who did not return to sport after ACLR reported poorer knee-related and health-related QOL, compared to people who returned to pre-injury levels of sport. Higher body mass index (BMI) and subsequent surgery were also related to worse QOL after ACLR.This was the first study to show that return to sport was associated with QOL impairment more than five years after ACLR. However, quantitative assessment of QOL may overlook important considerations with regard to an individual's life priorities, expectations, values and concerns.To provide a detailed understanding of QOL following ACLR, qualitative interviews were performed with 17 individuals with knee difficulties 5 to 20 years following ACLR. This was the first qualitative study to explore QOL following...