Significant changes have occurred in the approach to structural analysis over the last twenty years. These changes have been brought about by a more general understanding of the nature of the problem and the develop­ ment of the digital computer. Almost all s~ructural engineering offices throughout the world would now have access to some form of digital computer, ranging from hand-held programmable calculators through to the largest machines available. Powerful microcomputers are also widely available and many engineers and students have personal computers as a general aid to their work. Problems in structural analysis have now been formulated in such a way that the solution is available through the use of the computer, largely by what is known as matrix methods of structural analysis. It is interesting to note that such methods do not put forward new theories in structural analysis, rather they are a restatement of classical theory in a manner that can be directly related to the computer. This book begins with the premise that most structural analysis will be done on a computer. This is not to say that a fundamental understanding of structural behaviour is not presented or that only computer-based tech­ niques are given. Indeed, the reverse is true. Understanding structural behaviour is an underlying theme and many solution techniques suitable for hand computation, such as moment distribution, are retained. The most widely used method of computer-based structural analysis is the matrix stiffness method.