Community-acquired pneumonia (CAP) is a common and potentially serious disease as it is a cause of significant morbidity and mortality in adults. The annual incidence of pneumonia in the general population in adults is 5 to 11 cases per 1000 people. According to the published epidemiological studies the most common causes of CAP in Europe, Latin America and the US are Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydophila pneumoniae, Haemophilus influenzae, Enterococci and Legionella pneumophila. A new infiltrate on chest X-ray with typical clinical symptoms and signs is required for the diagnosis of pneumonia. Microbiological evaluation is not recommended for outpatient treatment. Empirical antibiotic therapy almost always reveals successful clinical outcomes. In hospitalized patients, especially with severe pneumonia, microbiological identification of bacteria can positively affect the therapeutic approach and the outcome of treatment. Therefore, blood cultures, urinary antigen tests for Legionella and pneumococus and sputum culture are indicated. It is recommended to take two blood cultures, especially in patients with specific indications, such as the Intensive Care Unit treatment. Blood cultures taken before starting the antibiotic treatment are positive in 7% to 16% of cases. Legionella and S. pneumoniae urinary antigen tests are recommended only in severe pneumonias. Despite microbiological tests, most hospitalized patients with CAP are without etiological diagnosis and are treated empirically. Two biomarkers, procalcitonin (PCT) and C-reactive protein (CRP) can help distinguish bacterial from viral infections. They can support a clinical decision on the initiation or discontinuation of antibiotic therapy. Persistently high PCT values suggest a poor prognosis. After confirming the diagnosis of pneumonia, it’s necessary to assess the severity of the disease and make a decision about either hospitalization or outpatient treatment. For this purpose multiple scoring systems, such as Pneumonia Severity Index (PSI) and CURB-65, are used in everyday practice.