GOOD ventilation is recognised as an essential for the preservation of health, and laws have accordingly been framed in many countries for the provision of adequate ventilation in factories and places of public resort as well as in mines. Apart from the legislative enforcement of hygienic measures as a matter of public policy, the ventilation of mines has an important economic aspect, since it affects to a large extent the industrial efficiency of the workmen, and consequently the cost of mineral production. Until recent years the ventilation of metal mines has not generally received much consideration, and the importance of pure air has been sometimes overlooked. To the absence of explosive gases in such mines, and to the cost of the installation and working of mechanical ventilators, may generally be attributed disregard of adequate ventilation. In this paper it is not proposed to furnish statistics on the mortality and morbidity of miners, or a treatise on the medical aspect of the rock-dust problem, to further elaborate which would be superfluous, the deleterious effects of the latter having been the subject of exhaustive scientific inquiry in many countries. It is proposed to consider the subject from a practical standpoint by a review of the standards of ventilation in operation, the most important scientific investigations, and of existing laws appertaining to ventilation.