These guidelines address the administration of systemic antibiotics in periodontics, especially in the treatment of periodontitis, necrotizing gingivitis/periodontitis, periodontal abscess and periimplantitis. Microorganisms associated with these conditions aggregate as structured biofilms on tooth surfaces, and biofilms effectively protect microorganisms from antibiotics. It is therefore a central principle to use antibiotics only as adjunct to mechanical debridement. In fact, many cases can be resolved by mechanical therapy even without the prescription of antibiotics. Good oral hygiene is crucial for longterm success.