Polymers are widely used in packaging and automobile industries because of their desirable properties such as lightweight, transparency, strength to weight ratio, good hardness and stiffness, low water absorption, ultraviolet rays' protection. Keeping Polymethyl methacrylate (PMMA) polymer in focus, this review research is being done here to collect the literature available best of our knowledge on the joining of PMMA to PMMA/Polymers/ Metal alloys by Friction stir welding/ Friction stir spot welding (FSW/FSSW). Friction stir welding is a solid-state joining process in which the temperature remains below the material's melting temperature. This friction stir welding technique is widely applied on materials that are difficult to weld by fusion welding, such as aluminium alloys, titanium alloys, and polymers. Friction stir welding is an ecological weld method and environmentally friendly as it does not produce harmful radiation toxic gases, requires less energy, produces less waste than conventional fusion welding processes. It was found out that by applying Friction stir welding/ Friction stir spot welding technique, the Polymethyl methacrylate can be welded to itself, to polymers, and metal alloys. In this review, efforts are made to point out the optimum level of process parameters of FSW concluded by researchers in their studies of PMMA joining. For each study, its parameter range and the optimum value of process parameters are presented in the form of tables and graphs, and explanations and discussions are made to better understand welding Polymethyl methacrylate polymer by Friction stir welding process.