Microbiological expertise is essential in the diagnosis, management, and prevention of infective endocarditis (IE). Unfortunately old habits die hard and there are still doctors who persist in referring to this infection as “SBE” (subacute bacterial endocarditis) whether the patient has been ill for days, weeks or months, and think that it is generally caused by a microbe they know as “Strep viridans” and can often be blamed on dentists. IE cannot be considered as a homogeneous infection. It may arise in the community or, increasingly, in hospital or as a result of procedures undertaken in hospital; it may affect native valves (previously normal or abnormal) or prosthetic valves and may occur in intravenous drug users (IVDU) as well as those who do not use drugs. Although overall most cases of IE are caused by staphylococci, streptococci, and enterococci, the incidence of each group of organisms differs in the various types of IE. A wide variety of organisms account for the infections not caused by these three genera, and virtually every organism known to microbiologists has been reported to cause IE, albeit very rarely. At St Thomas' Hospital, in some 650 cases of IE seen over 30 years we have encountered infections caused byErysipelothrix rhusiopathiae,Listeria monocytogenes,Campylobacter fetus,Lactobacillus rhamnosus, andHistoplasma capsulatum!