The aim of this monograph is to give a unified account of the classical topics in fixed point theory that lie on the border-line of topology and non­ linear functional analysis, emphasizing developments related to the Leray­ Schauder theory. Using for the most part geometric methods, our study cen­ ters around formulating those general principles of the theory that provide the foundation for many of the modern results in diverse areas of mathe­ matics. The main text is self-contained for readers with a modest knowledge of topology and functional analysis; the necessary background material is collected in an appendix, or developed as needed. Only the last chapter pre­ supposes some familiarity with more advanced parts of algebraic topology. The "Miscellaneous Results and Examples", given in the form of exer­ cises, form an integral part of the book and describe further applications and extensions of the theory. Most of these additional results can be established by the methods developedin the book, and no proof in the main text relies on any of them; more demanding problems are marked by an asterisk. The "Notes and Comments" at the end of paragraphs contain references to the literature and give some further information about the results in the text.