Bacterial pneumonia may be due to a variety of underlying causes. The microorganisms responsible are divided into typical and atypical. Typical bacteria often result in a classic pneumonia whereas atypical bacteria lead to a much milder presentation often referred to as “walking pneumonia“. These patients appear near normal but have extensive findings on chest x-ray. Apart from typical and atypical classifications, bacterial pneumonia can be categorized based on demographics by differentiating into neonates (<4 weeks old), toddlers (2 – 4 years), children (4 weeks – 18 years), adults (18 – 65 years), and the elderly (>65 years). Underlying characteristics may also help determine the specific cause. These include alcoholics, those at risk of aspiration, cystic fibrosis, intravenous drug users, and those that are immunocompromised or at risk of nosocomial pneumonia.