Prof Williams has expertise in the investigation and management of adults with a range of allergic disorders including anaphylaxis, latex allergy, venoms, urticaria and angioedema, immunotherapy and drug allergy. He also investigates and manages adults and children (jointly with paediatricians) with recurrent infections and unusual immune disorders. His clinical and research interests are in recurrent infections, allergen immunotherapy, anaphylaxis and developments in laboratory diagnostics for immunologically-mediated diseases.