With great potential in food and pharmaceutical applications, deep eutectic solvents (DES) are a green alternative to traditional toxic organic solvents. DES are developed from the combination of hydrogen bond donors (HBDs) and hydrogen bond acceptors (HBAs), creating a range of unique properties including low volatility, tunability, high solubility, and biodegradability. Their green nature renders them of special worth for sustainable processing, for example, in food use, DES facilitates effective and selective recovery of bioactive compounds such as polyphenols, flavonoids, alkaloids, and carotenoids from botanical sources. Additionally, their food-grade safety and antibacterial activity position them for value in preservation and functional food development. In the context of pharmaceuticals, DES are emerging as stars due to their capability to enhance the solubility, permeability, and stability of poorly water-soluble drugs. They have been promising to improve oral and transdermal drug delivery systems, aid in active pharmaceutical ingredient (API) crystallization, control polymorphism, and controlled release. Despite these advancements, it should be noted, however, that toxicity, mass production, and regulatory approval are still hurdles to overcome. This chapter discusses not only the chemistry, design, and applications of DES in food and pharmaceutical science but also their weaknesses and sustainability challenges. With made-to-order combination and formulation processes from frontier extraction technologies, DES has the potential to introduce greener, safer, and more efficient ways of working for the food and pharmaceutical sciences.