EN 1990 defines structural reliability as the ability of a structure to fulfil the specified requirements during the service life for which it has been designed; the notion covers safety, serviceability and durability. According to this definition reliability is the concern of all parts of the whole suite of Eurocodes. In a more narrow sense of the word, reliability refers to the way uncertainties are dealt with in design and assessment by the use of partial factors or more advanced probabilistic methods. This document deals primarily with this more narrow definition, it describes both the probabilistic and semi-probabilistic approach and gives special attention to their underlying relationship.Chapter 2 should be considered as a general introduction to this report and introduces relevant basic notions such as uncertainty, probability, risk, member and system failure, time dependency, effects of deterioration and inspection, etc. In chapter 3 the focus is on the basic reliability requirements in EN 1990 related to the persistent as well as the accidental and seismic design situations. Some special attention is given to the new materials: glass, fibre reinforced polymers and membrane structures included in the second generation of the Eurocodes.In chapter 4 attention is given to the special problems that may arise in assessment of existing structures. Important is the treatment of several types of observations (inspections, monitoring, proof loads etc), the various decision options (further inspection, repair, demolishment) and of course typical reliability issues (updating, reduced targets). The explicit risk and full probability methods described in Chapter 5 are intended to support these approaches where allowed and meaningful. It also gives background for code calibrations.Annex A gives an overview of probabilistic models for actions, material properties and model uncertainties. It may be considered as a reflection of the present state of knowledge in the various Eurocode subcommittees, working groups and horizontal groups. Annex B shows a number of example applications related to various parts of the theory.