This book is based on a number of lectures presented at CISM* -Course on "Stochastic Methods in Structural Mechanics", August 28 -30,1985 in Udine, Italy. The chapters presented here are either expanded and/or updated versions of these lectures. The purpose is to introduce readers to basic principles of stochastic methods of structural mechanics, particularly to those of dynamics. For those readers who wish to pursue the study further, the references provided in each chapter will serve as a useful source of information. Nevertheless the readers find some of the advanced topics presented by the authors immediately useful for their own application. The first section of Chapter 1 introduces the reader to the basic principles of probability theory followed by the discussion of methods to calculate time invariant structural reliability estimates, where the exact methods are particularly emphasized. The Chapter continues with a first introduction to the theory of stochastic processes. The properties of Gaussian and other type of processes are discussed. In dealing with observed data, tests of stationarity, as well as methods to estimate power spectra are described in some detail. The Chapter closes with a first treatice of excursions of stochastic processes in terms of number and duration of excursions, extremes, envelopes and time to first excursions. In Chapter 2 linear structures under stochastic loading are analyzed by applying the concepts as outlined in Chapter 1. The analyses are carried out in the time and frequency range respectively.