This paper discusses the development of a publicly available database of composite steel beam-to-column connections under cyclic loading. The database is utilized to develop recommendations for the seismic design and nonlinear performance assessment of steel and composite-steel moment-resisting frames (MRFs). In particular, the sagging/hogging plastic flexural resistance as well as the effective slab width are assessed through a comparison of the European, American and Japanese design provisions. The database is also used to quantify the plastic rotation capacity of composite steel beams under sagging/hogging bending. It is found that the Eurocode 8-Part 3 provisions overestimate the plastic rotation capacities of composite beams by 50% regardless of their web slenderness ratio. Empirical relationships are developed to predict the plastic rotation capacity of composite steel beams as a function of their geometric and material properties. These relationships can facilitate the seismic performance assessment of new and existing steel and composite-steel MRFs through nonlinear static analysis. The collected data underscores that the beam-to-column web panel zone in composite steel beam-to-column connections experience higher shear demands than their non-composite counterparts. A relative panel zone-to-beam resistance ratio is proposed that allows for controlled panel zone inelastic deformation of up to 10 times the panel zone’s shear yield distortion angle. Notably, when this criterion was imposed, there was no fracture in all the examined beam-to-column connections.