The disease of pulp and periapical tissue are most commonly encountered problems in the oral cavity. Most cases of pulpitis are primarily a result of dental caries. Infection of dental pulp spreads through the root canal into the periapical region which results in diseases of the periapical tissues. This chapter includes etiology and classification of pulpitis, diseases of periapical tissues which includes periodontitis, periapical granuloma, periapical cyst, residual cyst, periapical abscess.