This book presents 19 revised invited keynote lectures and revised tutorial lectures given by top-researchers at the 4th International Symposium on Formal Methods for Components and Objects, FMCO 2005, held in Amsterdam, Netherlands, in November 2005. The book provides a unique combination of ideas on software engineering and formal methods that reflect the current interest in the application or development of formal methods for large scale software systems such as component-based systems and object systems. The papers are organized in topical sections on component and service oriented computing, system design, tools, algebraic methods, model checking, assertional methods, quantitative analysis.