The aim of this research is to provide an alternative for the conventional design of beam-to-column connections in building structures. The new design is performed by means of Structural Topological Optimization and executed by means of additive manufacturing with steel. Regarding the methodology, the joint that would be manufactured by conventional methods (i.e. welded and bolted plates) is modelled by means of finite elements in the first place. Its behavior is obtained, as well as the boundary conditions and the loads to be applied to the part that is going to be optimized. Subsequently, a solid part is defined and optimized by means of the optimization module TOSCA. Then, the complete joint is simulated with the optimized connection, and the behavior and the weight of the material used are compared with those of the conventional joint.Some modifications are made to improve some aspects of the design. Afterwards, the optimized joint is printed with steel S316L, the connection is as-sembled with the columns and beams, and it is tested. The experimental results are analyzed to be able to make the necessary adjustments both in the connection and in the design methodology.