The presentation covers the history of the discovery and development of rational antimicrobial chemotherapy before describing the terms used in discussing antibiotics and antibiotic resistance. The tests used to determine susceptibility to antibiotics in the laboratory are described as are the possible interactions, both negative and positive, that may occur when more than one antibiotic is used. The concept of “selective toxicity” is introduced before the presentation moves on to consider the major targets for antibiotic action along with the drugs that exploit those targets. In the second part of the presentation, the focus moves to antibiotic resistance and the ways in which bacteria may resist antibiotics. The problem of resistance in meticillin-resistant Staphylococcus aureus is explored in detail and the presentation concludes with a discussion of the mobile genetic elements responsible for the spread of resistance.