Definition of semi-rigid steel structural connections, classification and influence to the structural response of sway and non-sway steel frames. Sources of connection compliance, ductility and the application of the component method for characterization of the joint properties. Verification procedures for the available and the required capacity of joints and the design of semi-rigid steel structural connections. Application of the Finite Element Method for the simulation of the structural response of semi-rigid connections taking into account all prominent nonlinear phenomena (cf. e.g. contact, friction and plasticity).