This thesis developed and piloted a suite of sustainability indicators for assessing the extent to which upland estate management in Scotland delivers sustainability goals. In Scotland, upland areas have a unique pattern of land ownership, with much of the land divided into ‘estates’ owned by private individuals and organisations, public bodies, and non-governmental and community organisations. Upland estate management objectives and land uses are wide-ranging - agriculture, forestry, nature conservation, property and sporting interests – set within discourses of sustainability and multifunctionality and also including new developments in tourism, renewable energy and biodiversity conservation. The complexity of upland estate management presents a great challenge, both theoretically and practically. To tackle this complexity, indicators were developed using a transdisciplinary research approach, combining academic and non-academic knowledge within a deliberative research process to address a ‘real world’ problem. A conceptual framework guided the adaptation of the Delphi technique so that the indicators were selected in a manner which: (1) increased transdisciplinary capacity; (2) facilitated knowledge integration; and (3) enhanced the potential for social learning. Using the adapted technique, the researcher facilitated an anonymous, iterative research process that took place over four rounds, and involved a mixed panel of individuals who comprised expertise in sustainability, rural and upland land use, and estate management. A contemporary and consensual definition of ‘sustainable upland estate management’ was developed by the panel, through the identification of five ‘sustainable estate principles’ (Adapting Management; Broadening Options; Ecosystem Thinking; Linking into Social Fabric; Thinking beyond the Estate) and 16 corresponding indicators (‘opportunities for sustainable estates’) within a ‘Sustainable Estates Toolkit’. The anonymous nature of the process created a safe environment for open dialogue and the researcher played an active role in stimulating participant motivation, creativity and learning.