Legionellae, which are important causes of pneumonia in humans, continue to be incorrectly labeled as exotic pathogens. The ability to diagnose Legionella infection is limited by the nonspecific nature of clinical features and the shortcomings of diagnostic tests. Despite recent improvements, existing diagnostic tests for Legionella infection either lack sensitivity for detecting all clinically important legionellae or are unable to provide results within a clinically useful time frame. Understanding local Legionella epidemiology is important for making decisions about whether to test for Legionella infection and which diagnostic tests to use. In most situations, the use of both the urinary antigen test plus sputum culture is the best diagnostic combination. Polymerase chain reaction (PCR) is a promising tool, but standardized assays are not commercially available. Further work needs to focus on the development of urinary antigen tests assays that detect a wider range of pathogenic legionellae and on the development of standardized PCR assays.