At present, it is well known that oral health is essential for the well-being of the body as a whole, thanks to the increasing awareness of how various oral diseases, including periodontal disease, oral carcinomas, and other conditions, have a close connection with various systemic disorders. In recent decades, studies on the oral microbiome have increasingly emphasized how the balance between the host and the microbial species that coexist there is essential for oral health at all stages of life. However, there are many factors capable of interfering with that balance, and diet is precisely one of them. The real influence of diet on the oral microbiota, and consequently on oral health, has been much debated. In this context, the observation of two key periods in human history, the Neolithic and the Industrial Revolution, has proved to be diriment. The foods and processing techniques that emerged in these two historical periods, in association with changes in customs and habits, significantly altered the central constituents of the human diet, including macronutrient proportions, glycemic load, fatty acid composition, sodium and potassium levels, micronutrient levels, dietary pH, and fiber content taken in by human beings. The introduction of these foods into the daily human routine has been linked to a decline in oral health and an increase of several other diseases, including cardiovascular diseases, inflammatory bowel disease, rheumatic diseases, many cancers, and obesity. The aim of this chapter is to update the current knowledge and further discuss the role of diet and nutrition on oral health.