B is a method for specifying, designing and coding software systems. It is based on Zermelo-Fraenkel set theory with the axiom of choice, the concept of generalized substitution and on structuring mechanisms (machine,refinement, implementation). The concept of refinement is the key notion for developingB models of (software) systems in an incremental way. B models are accompanied by mathematical proofs that justify them. Proofs of B models convince the user (designer or specifier) that the (software) system is effectively correct. We provide a survey of the Event B method and the semantic concepts related to the B method; we detail the B development process partially supported by the mechanical engine of the prover. Case studies are illustrating the Event B method.