Tonsillitis, or inflammation of the tonsils, makes up approximately 0.4% of outpatient visits in the United States. Tonsillitis is caused by a viral infection in 70% to 95% of cases. However, bacterial infections caused by group A beta-hemolytic streptococcus (Streptococcus pyogenes) account for tonsillitis in 5% to 15% of adults and 15% to 30% of patients five to 15 years of age. It is important to differentiate group A beta-hemolytic streptococcus from other bacterial or viral causes of pharyngitis and tonsillitis because of the risk of progression to more systemic complications such as abscess, acute glomerulonephritis, rheumatic fever, and scarlet fever after infection with group A beta-hemolytic streptococcus. A variety of diagnostic tools are available, including symptom-based validated scoring systems (e.g., Centor score), and oropharyngeal and serum laboratory testing. Treatment is focused on supportive care, and if group A beta-hemolytic streptococcus is identified, penicillin should be used as the first-line antibiotic. In cases of recurrent tonsillitis, watchful waiting is strongly recommended if there have been less than seven episodes in the past year, less than five episodes per year for the past two years, or less than three episodes per year for the past three years. Tonsilloliths, or tonsil stones, are managed expectantly, and small tonsilloliths are common clinical findings. Rarely, surgical intervention is required if they become too large to pass on their own.