β-Lactamase production is responsible for the appearance of a large number of pathogenic bacterial strains exhibiting a high degree of resistance to β-lactam antibiotics. A large number of enzymes have been described with very diverse primary structures and catalytic profiles. Nevertheless, all known three-dimensional structures of active-site serine β-lactamases exhibit a high degree of similarity with apparently equivalent chemical functionalities in the same strategic positions. These groups might not, however, play identical roles in the various classes of enzymes. Structural data have also been recently obtained for the zinc metallo-β-lactamases, but the detailed catalytic mechanisms might also differ widely, depending on the enzyme studied. Similarly, the induction of the synthesis of β-lactamases is now better understood, but many questions remain to be answered.