Community-acquired pneumonia is a frequent cause of morbidity, hospitalization and death especially among patients with risk factors. Several agents can provoke this condition and their relevance change according to specific epidemiological exposures, time of the year and comorbidity, being Streptococcus pneumoniae the most frequent etiological agent followed by Mycoplasma pneumoniae, Chlamydia pneumoniae, respiratory viruses and Haemophilus influenzae. Management requires proper identification of the most vulnerable patients and prompt admittance and X-ray confirmation to analyze extension, complications or differential diagnosis. Etiological studies are limited by the low sensitivity and specificity of the sputum Gram stain, the invasive nature of some techniques or the high cost of a comprehensive study. Nonetheless, etiological studies are relevant on severe cases, immunosuppressed patients or those without response to an empirical treatment. New diagnostic tests include serological studies for atypical pathogens, direct detection of viral agents or pneumococcal antigens on sputum samples and Legionella pneumophila serotype 1 antigen detection in urine. Penicillin resistant pneumococcal (PRP) isolates associated to pneumonia or bacteremia as well as isolates with resistance to third generation cefalasporins or macrolides are still infrequently observed among adult patients in Chile. Notwithstanding, worldwide experience indicates that patients affected by PRP isolates and treated with penicillin do not evolve with a higher risk for treatment failure, except for those cases where the MIC for penicillin is equal or higher than 4 µg/mL.