This study investigates differences in molar wear patterns between hunter-gatherers and agriculturalists, suggesting that these differences are related to variations in diet and food preparation methods. The research compares the flatness of molar wear in five groups of hunter-gatherers (N = 298) and five groups of early agriculturalists (N = 365). Hunter-gatherers are predicted to develop flatter molar wear due to the mastication of tough and fibrous foods, whereas agriculturalists should develop oblique molar wear due to an increase in the proportion of ground and prepared food in the diet. A method is presented for the quantitative measurement and analysis of flatness of molar wear. Comparisons of wear plane angles are made between teeth matched for the same stage of occlusal surface wear, thus standardizing all groups to the same rate of wear. Agriculturalists develop highly angled occlusal wear planes on the entire molar dentition. Their wear plane angles tend to exceed hunter-gatherers by about 10° in advanced wear. Wear plane angles are similar within subsistence divisions despite regional differences in particular foods. Tooth wear is a skeletal feature that preserves direct evidence of the masticatory behavior of mammals. Mastication is intimately related to diet, and patterns of tooth wear can be used to make inferences about diet in prehistoric populations and extinct species. From an anthropological point of view, tooth wear may record important stages in human biological and cultural evolution, including evidence of food resources utilized by ancestral hominids, development of fire and cooking, invention of food processing utilizing grinding tools, adoption of agriculture, invention of pottery, and other refinements in the way food is processed. The study found that agriculturalists develop more oblique wear planes than hunter-gatherers, which is attributed to a reduction in food toughness or fibrousness associated with the appearance of intensive collection of grains and intensive use of grinding stones and pottery in food preparation. Flatness of molar wear appears to be a good indicator of change in food or food preparation. This pattern and other features of tooth wear can be used to support dietary inferences at important points in cultural and technological evolution in humans, and to illuminate changes in mastication and diet in earliest hominids.This study investigates differences in molar wear patterns between hunter-gatherers and agriculturalists, suggesting that these differences are related to variations in diet and food preparation methods. The research compares the flatness of molar wear in five groups of hunter-gatherers (N = 298) and five groups of early agriculturalists (N = 365). Hunter-gatherers are predicted to develop flatter molar wear due to the mastication of tough and fibrous foods, whereas agriculturalists should develop oblique molar wear due to an increase in the proportion of ground and prepared food in the diet. A method is presented for the quantitative measurement and analysis of flatness of molar wear. Comparisons of wear plane angles are made between teeth matched for the same stage of occlusal surface wear, thus standardizing all groups to the same rate of wear. Agriculturalists develop highly angled occlusal wear planes on the entire molar dentition. Their wear plane angles tend to exceed hunter-gatherers by about 10° in advanced wear. Wear plane angles are similar within subsistence divisions despite regional differences in particular foods. Tooth wear is a skeletal feature that preserves direct evidence of the masticatory behavior of mammals. Mastication is intimately related to diet, and patterns of tooth wear can be used to make inferences about diet in prehistoric populations and extinct species. From an anthropological point of view, tooth wear may record important stages in human biological and cultural evolution, including evidence of food resources utilized by ancestral hominids, development of fire and cooking, invention of food processing utilizing grinding tools, adoption of agriculture, invention of pottery, and other refinements in the way food is processed. The study found that agriculturalists develop more oblique wear planes than hunter-gatherers, which is attributed to a reduction in food toughness or fibrousness associated with the appearance of intensive collection of grains and intensive use of grinding stones and pottery in food preparation. Flatness of molar wear appears to be a good indicator of change in food or food preparation. This pattern and other features of tooth wear can be used to support dietary inferences at important points in cultural and technological evolution in humans, and to illuminate changes in mastication and diet in earliest hominids.