A great variety of building stones were used in Venice. Different weathering phenomena can be observed on each type of stone. Since air pollution is considered one of the main factors contributing to stone decay, extensive measurements of air pollutants have been taken. The joint action of natural weathering and attack by acid pollutants is a main reason for the rapid decay of monuments. Different experts have applied various stone consolidation techniques. In addition to the early application of oils and fats to protect the stone from humidity, recently PVA emulsions, polysiloxanes, fluorosilicates, Lewin's BaOH-urea method, and microcrystalline waxes had been used. Also, different cleaning techniques have been applied. -- AATA