The objectives of the thesis are – (a) to identify the problems in water-energy-food nexus from ICT and Law point of view and to propose theoretically a legal knowledge framework for water-energy-food nexus in order to reduce those problems technologically, (b) to construct and implement legal ontology for nexus extracted from EU water, energy and food Regulations in OWL 2 language, which is a part of the grater work of implementing legal knowledge framework for water-energy-food nexus proposed through the compilation of objective (a). Considering these objectives, this thesis presents total five chapters. First chapter investigates current start of art of nexus in order to identify (1) major knowledge gaps in the nexus and (2) ontological existence of the nexus in the EU regulations, particularly in the legal definitions accommodated in EU Regulations and Directives associated with nexus domains. It also rationalizes the need for legal ontology for nexus. Second chapter evaluates existing perspectives and methodologies available for constructing legal ontology. The purpose of such evaluation was to select correct perspective and methodology for constructing legal ontology for nexus. It, at the end, justifies the need for developing new methodology for constructing the legal ontology for nexus. Third chapter explains the methodology used for engineering legal definitional knowledge extracted from the selected EU regulations in order to construct the legal ontology for nexus. Fourth chapter explains in detail the legal ontology for nexus while fifth chapter evaluates legal ontology for nexus. In addition, conclusion of the thesis shares critical issues faced throughout this doctoral thesis work. Furthermore, annexes contain a list of all formulas of restrictions implemented in legal ontology for nexus and links of all modules of legal ontology for nexus. LODE documentation of the legal ontology for nexus is available at http://codexml.cirsfid.unibo.it/post-doctoralresearchers/mizanur-rahman/