Polymer-based composites have gained prominence in tribological applications due to their lightweight nature, tunable properties, and multifunctional potential. However, existing reviews largely report performance improvements without systematically addressing contradictory trends, testing variability, and emerging manufacturing routes. This review analyses friction and wear mechanisms in fibre-reinforced and particle-reinforced polymers, surface coatings, and additively manufactured polymer composites. Key mechanisms, including load transfer, transfer film formation, thermal dissipation, and interfacial effects, are critically synthesised across thermoset and thermoplastic systems. Representative performance trends are discussed to highlight the influence of reinforcement type, processing route, and operating conditions, along with limitations in current tribological testing practices and the need for standardisation. By integrating mechanistic understanding with comparative performance and future research priorities, this review provides guidance for the design and evaluation of polymer composites in automotive, aerospace, marine, and biomedical tribological applications.