Community-acquired pneumonia (CAP) is defined as an acute infection of pulmonary parenchyma in a patient who has contracted the infection in the community. Diagnostic process includes history taking, physical examination, chest radiograph, blood tests, and microbiologic tests. Common clinical features are cough, sputum, fever, pleuritic chest pain, and dyspnea. There are systemic symptoms such as nausea, vomiting, diarrhea, and changes of mental status. The presence of an infiltrate on chest X-ray is the mainstay for the diagnosis of CAP, although exceptions are early CAP, dehydration, and neutropenia. Prevalent radiographic findings are lobar pneumonia, interstitial infiltrates, and cavitation. Performing diagnostic testing for the microbiologic etiology remains controversial particularly in outpatient settings. The tests are recommended only when pathogens that would not respond to usual empirical antibiotic regimens are suspected. However, for hospitalized patients, routine pursuit of etiologic agents should be done for all occasions. Apart from Gram stain and culture of sputum, blood culture, serologic tests, urine antigen tests, and polymerase chain reactions are being performed in hospitalized patients. Among these, the combination of a good sputum specimen for Gram stain and culture plus urinary antigen testing is most useful for the rapid diagnosis of CAP. The positivity rate of blood culture is relatively low, which makes the test less dependable. We should always consider Mycobacterium as an unpredicted cause of pulmonary infiltrates in Korea. We should also bear in mind unusual pathogens that have an epidemiologic significance or need different regimens from empirical antibiotics. These include Influenza, Legionella, community-acquired methicillin-resistant Staphylococcus aureus, and agents of bioterrorism. In conclusion, any diagnostic tests should not delay the administration of proper antibiotics. Comprehensive knowledge regarding the relevant diagnostic tests is required for the appropriate implementation of diagnostic procedures and empirical antibiotics.