For centuries, the dominant form of waste disposal has been landfill, however, this is now deemed to be non-viable from a social, legislative, environmental and economic perspective. Therefore, more sustainable methods of waste disposal are needed globally to reduce the amount of waste going to landfill (e. g. composting). This thesis considered two different forms of in-vessel composting and their effectiveness in treating the biodegradable fraction of Municipal Solid Waste (MSW) that had been mechanically separated prior to composting in two areas of Wales. Further to this, the potential for using MSWbased composts as growth media was investigated alongside the physical composition of MSW-based composts. This thesis found that primary-screened MSW contained a high amount (>50%) of biodegradable matter with varying amounts of glass (ca. 23%), plastic (ca. 10%) and other components present. Both in-vessel composting methods were successful at treating MSW and produced composting profiles similar to those for green waste (e. g. increased pH, reduced EC and increased N03" content). Alongside this, both methods also reached temperatures high enough to cause destruction of human enteric pathogens making them compliant with the 2005 Animal By-Products Regulations. Inert matter (i. e. glass and plastic) remained unchanged during composting, but beneficially enhanced composting by improving aeration. In contrast, small bench-scale composting units failed to realistically mimic the performance of the larger scale MSW composting systems; the results obtained with them suggested that commercial composting additives did not enhance the rate of composting. The use of the MSW-based growth media showed that as the materials matured, yields of two common pasture land species increased significantly, and in some cases exceeded those of commercially available growth media used widely in horticulture. Combining agricultural soils with these MSW-based materials gave increased plant yields in comparison to soil alone, however, the benefits were dependent on the amount and type of MSW compost added. Further research is needed into the removal of physical and chemical contaminants from the parent materials for composting of MSW based materials along with clearer legislative definitions as to the possible end uses for such materials. The presence of clear markets has the potential to drive improvements in the technology used for MSW composting. In conclusion, composting provides a viable method for the treatment of MSW-derived biodegradable waste and has the potential to form an important component of sustainable waste management in the UK.