The life cycle assessment (LCA) of a waste management system relies on many internal characteristics such as pollution control systems and recovery efficiencies. It also relies on technical externalities supporting the waste management system in terms of capital goods and energy and material production systems. In the past, capital goods have often been disregarded because of a lack of time and assumptions of lower environmental impacts from these capital goods compared to the total impacts of waste management. However, capital goods have not been addressed in detail in the literature until now, and neglecting them may lead to an improper assessment of the environmental impacts of an entire waste management system. Another technical externality lies in the primary materials production systems required when producing secondary materials substitutes for primary materials. External databases are available today to model these primary material production processes, but their data quality varies. The aim of this PhD project was to find the relevance and importance of technical externalities in LCA of waste management systems. To provide a thorough overview on this issue, two research questions were explored: • How do capital goods contribute to the total environmental impacts of waste management systems? • What are the quality and consistency of data in external databases for the primary and secondary production of materials? Capital goods were quantified in detail for several technologies usually found in modern waste systems: a composting plant, an anaerobic digestion plant, an incinerator and landfill. As transportation and collection are important parts of waste management systems, their associated capital goods were also quantified in the terms of bins, containers and trucks. The results from the LCAs of full waste management systems revealed that capital goods should be included in future LCAs. The impact share of capital goods was highest for resource depletion and the impacts of toxicity on humans and ecosystems. To evaluate the quality and consistency of available data for the primary and secondary production of materials, 366 datasets were gathered. The materials in focus were: paper, newsprint, cardboard, corrugated board, glass, aluminium, steel and plastics (HDPE, LDPE, LLDPE, PET, PS, PVC). Only one quarter of these data concerned secondary production, thus underlining a severe lack of data for these production processes. The results showed large variations in CO2 emissions from the production of each of the evaluated materials. An evaluation of the data revealed that energy systems are central to impacts and are thereby important to specify as background information. A critical lack of background information in external databases was highlighted as well as a lack of transparency. Therefore, the assessment of the quality of data was difficult when no description was available. Some industries and branch organisations provide data for databases, which improves the quality of the available inventories, so LCAs would represent the industry better if consensus was found in industry and branch organisations regarding the provision of data for the LCA community or if the ISO standard for producing inventory data were followed, which in turn would help to increase transparency. In conclusion, technical externalities are important when considering the results of waste management LCAs. When technical externalities are included it is important that the background information is adequate, since the quality of the data will determine the quality of the results.