A lactam (the noun is a portmanteau of the words lactone + amide) is a cyclic amide. Prefixes may indicate the ring size: β-lactam (4-membered), γ-lactam (5-membered), δ-lactam (6-membered ring). That order in the nomenclature is because beta β, gamma γ and delta δ are the second, third and fourth letters in the alphabetical order of the Greek alphabet, respectively.
General synthetic methods exist for the organic synthesis of lactams.
- Lactams form by the acid-catalyzed rearrangement of oximes in the Beckmann rearrangement.
- Lactams form from cyclic ketones and ammonia in the Schmidt reaction.
- lactams form from cyclisation of amino acids.
- In iodolactamization  an iminium ion reacts with an halonium ion formed in situ by reaction of an alkene with iodine.
- Lactams form by copper catalyzed 1,3-dipolar cycloaddition of alkynes and nitrones in the Kinugasa reaction
- Lactams can polymerize to polyamides.
- β-lactam with a four-membered ring found in beta-lactam antibiotics. Penicillin, considered the most famous antibiotic, is a β-lactam antibiotic.
- Lactone, a cyclic ester.