The three broad cause categories of pneumonia are typically summarized as bacteria, viruses, and fungi. Bacterial pneumonia is common in adults and may require antibiotic therapy. Viral pneumonias (influenza, RSV, etc.) can surge during seasonal outbreaks and may predispose to secondary bacterial infection. Fungal pneumonia is less common and is more often seen in immunocompromised patients. This classification directly informs treatment logic—antibiotic vs antiviral vs antifungal strategies alongside supportive care. In real-world management, the key is to match the most likely category to the patient’s risk profile and refine the working diagnosis using testing and clinical reassessment when appropriate.