The working paper provides a legal definition of non-standard work and an overview of legally possible non-standard work relationships under Belgian legislation. The adopted legal definition allows to consider standard and non-standard work also in terms of access to the social security schemes. The legal definition of non-standard work relies on five alternative and non-mutually exclusive criteria, namely (1) part-time employment relationships, (2) multipartite or triangular employment relationships, (3) temporary employment relationships, (4) work relationships that do not involve the exchange of work for pay, and (5) work relationships without legal subordination. An additional criterion has been identified and consists of (6) the existence of an ad-hoc derogatory social security regime resulting in a lack of or partial coverage. This criterion makes it possible to account for weaker social security coverage that is not the indirect result of labour law characteristics. Criterion (6) is not sufficient by itself to qualify a work relationship as a non-standard one. Subsequently, the different non-standard work statuses that exist in the Belgian legal framework are explained, distinguishing between non-standard forms of work that involve one or multiple employment contracts on the one hand and forms of non-standard work outside an employment contract on the other hand. ; The CHANGE project is a research project between the Herman Deleeck Centre for Social Policy (CSB, University of Antwerp, coordinator), the Centre for Public and Social Law (CDPS, Université Libre de Bruxelles), and the Centre for Sociological Research (CESO, KU Leuven). This collaborative initiative is driven by a partnership between academic institutions and funded by BELSPO, the Belgian Science Policy Office under the BRAIN-be program. The core mission of the project is to comprehensively examine and address the challenges faced by non-standard workers within the social protection system. These workers, including the self- employed, ...