The complexity of resource management often demands an integration of transdisciplinary methods to find sustainable solutions. This doctoral thesis aims at contributing to the science of resource management through the applications of systems engineering (SE). The case of marine plastic waste from commercial fishing gears (FGs) is used to demonstrate the application of the adapted SE framework. Marine plastic is a complex transboundary problem adversely affecting the coastal and marine ecosystems. Among the total marine plastic waste, Abandoned, Lost or Discarded Fishing Gears (ALDFG) is a particularly troublesome waste fraction that continues to trap marine life for years upon release and has significant adverse environmental effects on marine wildlife. However, lack of scientific data hinders the management of FG resources across the globe. The thesis aims to fill the knowledge gap through the application of SE to identify stakeholders and values, map their needs, and alternatives to support decision-making and evaluation. Contrary to traditional resource management studies, involvement and engagement of resource users are prioritized in this thesis to achieve the desired goal of sustainable life cycle management of FG resources. A life cycle of six FGs commonly deployed by the Norwegian commercial fishing fleet, trawls, seines (Danish and Purse), longlines, gillnets, and traps, is studied. Structured, semi-structured interviews and questionnaires were used for collecting information from key stakeholders. Based on data from gear producers, suppliers, fishers, collectors, authorities, and waste management facilities, annual flows of plastic polymers (PP, PE, and Nylon) from fishing gears are modelled. The thesis furthermore explores the application of multi-criteria decision analysis (MCDA) to assess end-of-life management alternatives based on the values of sustainability. Sustainable Development Goals and the EU's circular economy (CE) strategy are used for outlining the values for sustainability. The insights from stakeholders were used to ascertain potential barriers and opportunities in establishing circular business models in the region. The main contributions of this thesis are: •Adaption and application of SE for problem structuring •Development of research methods to extract information through active engagement of resource users •Modelling annual plastic flows across the system life cycle of commercial FGs used in Norway •Adaption of MCDA to assess sustainability in the end-of-life management of FGs •Identification of opportunities and barriers in realizing CE strategies for FG resources in Norway