The book "Formal Methods and Software Engineering" offers a comprehensive examination of formal methods for the development of computer systems. It highlights advancements in the application of semantic theories, specification languages, design techniques, as well as verification methods and tools that are significant for critical applications. The challenge lies in scaling these formal methods and integrating them into the engineering development processes to ensure the correct and efficient construction and maintenance of computer systems. The volume includes contributions from the 11th International Conference on Formal Engineering Methods (ICFEM 2009), which took place from December 9 to 11, 2009, in Rio de Janeiro. Researchers and practitioners from industry, academia, and government are invited to engage with the latest developments and challenges in this field.