The conception of net zero energy buildings (NZEB) has been introduced to limit energy consumption, global warming potentials, and pollution emissions in buildings. The challenge in NZEB design is to find the best combination of design strategies that will enhance the energy performance of a particular building. The aim of this thesis is to develop an understanding of NZEBs design concepts. Besides, it aims to assist NZEB designers to select the suitable design options of passive and RE systems based on a systemic evaluation in different climates. This thesis presents a methodology for the simulation-based multi-criteria optimization of NZEBs. The methodology is applied to investigate the cost-effectiveness potential for optimizing the design of NZEBs in different case studies taken as diverse climatic zones. The proposed methodology is a useful tool to enhance NZEBs design and to facilitate decision making in early phases of building design. A comprehensive study on optimal passive design for residential buildings is presented. The occupants’ adaptive thermal comfort is also improved by implementing the appropriate passive cooling strategies such as blinds and natural ventilation. The configurations and capacities of the implemented RE systems in NZEBs must be appropriately selected to ensure the intended performance objective. In the thesis, investigation, optimization and comparison of six RE solution sets for designing NZEBs is carried out in three typical climates: Indore (cooling dominant), Tromso (heating dominant) and Beijing (mixed climate).