The utilization of post-production and post-processing by-products aligns with current trends in sustainable fruit industry practices. Recovering valuable nutrients from such materials holds significant potential for the food, nutraceutical, pharmaceutical, and cosmetic sectors. Among these, cornelian cherry (Cornus mas L.) seeds represent a promising source of functional ingredients, particularly due to their oil’s rich nutritional and phytochemical profile. The seeds, accounting for approximately 9–10% of the fruit mass, yield an oil characterized by high levels of polyunsaturated fatty acids—mainly linoleic acid (≈67.5%) and oleic acid (≈20%)—alongside palmitic (≈5.8%) and stearic acids (≈2.1%). Linolenic acid content, however, shows notable variability (1.4–14.7%), influencing the oil’s omega-6/omega-3 ratio, which generally remains below 5:1. Cornelian cherry seed oil stands out among other stone fruit oils (e.g., rosehip, apricot, peach, cherry, plum) for its favorable fatty acid composition and absence of cyanogenic glycosides, making it safe for human consumption. Beyond its nutritional value, this oil exhibits biological activity and health-promoting potential, suggesting wide applicability in functional foods and nutraceutical formulations. Despite progress in characterizing seed composition—including proteins, lipids, carbohydrates, minerals, and tannins—knowledge gaps persist regarding the transfer of these compounds into the oil, particularly under cold-pressing conditions. Future studies should focus on optimizing extraction processes, assessing thermal treatment effects, and clarifying the variability of linolenic acid. Such research will support the sustainable exploitation of cornelian cherry by-products and the industrial-scale development of this high-value oil.