Abstract A review of representative metallogentic provinces brings out present trends in the interpretation of ore deposits and touches upon many major problems of ore deposition. The individual provinces vary in size from single mining districts to regions several hundred miles in extent; the limits usually are difficult to place. The great molybdenite deposits of Climax, Colorado, may be classed as a single molybdenite province or it may be considered as a part of the larger, more varied Front Range mineral belt. The ore deposits of the Peruvian Andes contrast with those of the Eastern Cordillera of Bolivia, yet gradations exist that suggest a certain unity to the mineralization. Some geologists describe the copper deposits of Northern Rhodesia and Katanga as a well-defined metallogenetic province, whereas others look upon these deposits as a part of the larger mineralized region that includes the uranium-copper-cobalt ores of Shinkolobwe and the copper-zinc ores of Kipushi. The association of the ores of Sudbury, Cobalt and Keweenaw Point with basic igneous rocks of late Precambrian age suggests a logical grouping of the deposits as a unit, although the processes of ore deposition may be quite distinct. Among the larger metallogenetic provinces that seem to be well established are those of the Coast Range of British Columbia and Alaska, the Sierra Nevada, and the copper belt of Chile and southern Peru. Of somewhat smaller size, the gold province of South Africa is more sharply defined. The age of ore deposition constitutes a major problem in many of the metallogenetic provinces under review. Some districts may permit a close dating of the ores and may give evidence of more than one metallogenetic epoch. In many districts, however, the age of the mineralization is fixed only within broad limits and is based largely on indirect evidence. This may lead to a difference of opinion as to the age of the mineralization and the number of epochs that are represented. In the San Juan region of Colorado, two distinct metallogenetic epochs are clearly established. In the Arizona-New Mexico province the deposition of copper took place during more than one metallogenetic epoch, although some question remains as to the exact age of certain deposits. The varied ore deposits of Idaho, grouped as a single metallogenetic province, illustrate the difficulty in the dating of ores. The principal deposits may be of Nevadan or of Laramide age; the ores of shallow type may represent one or two subsequent epochs of metallization. Studies elsewhere in the West suggest that the metallogenetic epochs are not so sharply defined as previously supposed. The close connection between basic magmas and the chromite, nickel-copper and titaniferous iron Ores is well established, although relatively few deposits are of strictly magmatic type. The possible connection between ore deposits and nearby granitic intrusions has been the subject of closer analysis. In the Precambrian districts of Canada, for example, the distribution of the massive sulfide deposits suggests that they are more closely related to the Keweenawan basic intrusions than to the Algoman granites. Ore deposits occurring in regions that show little evidence of intrusive igneous activity are difficult to explain. To account for these deposits, several theories have been stressed as alternatives to the hydrothermal theory and have been applied to the uranium ores of the Colorado Plateau, the copper deposits of Northern Rhodesia, the gold deposits of South Africa, and the iron ores of metamorphic terranes. Metallogenetic provinces outlined by deposits of sedimentary origin are well illustrated by the iron-formations of Precambrian age; there is substantial agreement that these formations represent chemical sediments. The possible correlation between epigenetic ore types and tectonic environments is being given increased attention. Characteristic of the highly metamorphic Precambrian terrane are deposits of high to moderate intensity, including gold-quartz veins, massive sulfide deposits, and various types of iron ores. Some of these can be duplicated in the more deeply eroded orogenic belts of later age, such as the Sierra Nevadas and Appalachians. In less deformed Precambrian rocks, ores of lower intensity prevail, as illustrated by the uranium, copper-cobalt and native copper deposits. In the younger mountain ranges, the ores are more varied and represent a wide temperature range, with many examples of lateral zoning. The ores correlated with the post-tectonic period of volcanism are perhaps the most distinctive: the gold-silver ores of the bonanza type, mixed base-metal ores, and uncommon metal combinations which reflect a high degree of telescoping. At the low-temperature end of the sequence are deposits characteristic of the stable regions: the lead-zinc, copper-cobalt, uranium, barite and fluorite deposits, many of which lie far from exposed igneous rocks. In many districts, careful study has revealed highly significant stratigraphic and structural controls in ore deposition that are not readily apparent. This is true not only of the complex metamorphic areas of the Precambrian and the highly deformed belts but also of areas of mild deformation where details of stratigraphy may be of utmost importance. The continued application of the principles of geochemistry, geophysics and geology, combining field and laboratory study, should be of value not only in determining the origin of the ores but also in explaining the metallogenetic provinces.