This is a textbook introduction to the B-Method, a rigorous methodology for the development of correct software, underpinned by powerful state-of-the-art tool support. It covers the B approach to software development from specification through refinement, down to implementation and automatic code generation, with verification at each stage. The book assumes no prior knowledge and is written in a tutorial style, containing numerous illustrative examples, exercises and self tests with answers. It also comes with a free licence for the B Toolkit.