The strong CP puzzle and axions

In the first part of this talk, after a brief presentation of the strong CP puzzle, the construction of axion models and their main phenomenological features are described. In the second part, the possibility to mix the Peccei-Quinn symmetry with baryon and lepton numbers is discussed, showing that the axion could ultimately play a role in other puzzles of the Standard Model like the smallness of neutrino masses or baryogenesis.