The durability of concrete structures is mainly affected by the transport of gaseous and liquid substances through its pore system which can potentially cause deterioration of the concrete. Thus, an important indicator of long-term durability is the relative ease with which each aggressive substance is transported through the concrete, in other words, its permeability. Studies were conducted to deepen knowledge of concrete permeability and, in particular, to understand how it is affected by the water-cement ratio, preconditioning temperature and testing pressure. The water-cement ratio is one of the main factors affecting concrete permeability; small changes in this ratio promote large permeability variations. An important increase of air permeability with the water-cement ratio and preconditioning temperature has been noticed. On the other hand, insignificant differences have been observed in the air permeability coefficient at the four testing pressures.