  Industrial applications involving formal methods are still exceptions to the
general rule. Lack of understanding, employees without proper education,
difficulty to integrate existing development cycles, no explicit requirement
from the market, etc. are explanations often heard for not being more formal.
Hence the feedback provided by industry to academics is not as constructive as
it might be. Summarizing a 25-year return of experience in the effective
application of a formal method - namely B and Event-B - in diverse application
domains (railways, smartcard, automotive), this article makes clear why and
where formal methods have been applied, explains the added value obtained so
far, and tries to anticipate the future of these two formalisms for safety
critical systems.
