Publications oriented to the interests of engineering scientists and graduate students on topics of functional analysis and its applications are rare - this book has been written to fill the gap in the literature. It provides a readable account of basic mathematic topics, with illustrative examples and chapters devoted to finite elements, variational principles of elasticity and plasticity, variational inequalities and elastic stability. The text is entirely self-contained and covers a wide range of topics and ideas, from elementary concepts to modern theories and applications, and includes numerous references. It is written for engineers, graduate students and researchers who need a general knowledge of modern mathematical methods in solid mechanics.