The evolution of tall buildings has taken place worldwide, starting in the United States in the twentieth century, from the conventional moment resisting frame to more effective structural systems, such as brace tubes and diagrid structures. In this Thesis, attention has been paid on diagrid structures. Their capacity to withstand lateral loads, despite the lack of vertical columns along the external perimeter of the building, has made the diagrids highly appreciated in the fields of structural engineering and architecture. In particular, many researchers have emphasized their enhanced performance and ground-breaking aesthetic characteristics. The main purpose of the study is to identify the optimal diagrid geometry able to ensure simultaneously a good structural behaviour, in terms of lateral and torsional stiffness, low consumption of material and feasibility of construction.