Carotenoids are versatile isoprenoid compounds biosynthesized by photosynthetic organisms as well as by some bacteria, fungi and arthropods. Most animals can incorporate them through the diet. They play key roles in photosynthesis and ecology that make them key for food security. They can also be metabolized into many compounds including phytohormones and other signals that play important roles in plants, some of them of great importance for their development and resilience and therefore also for food security. Their interest in foods is due to their roles as pigments, vitamin A precursors (some of them) and also as health-promoting compounds. Recently there is a renewed interest in their use with cosmetic purposes. Ulva is a good source of carotenoids, including lutein and β-carotene, which are among the main dietary carotenoids. In this contribution, the importance of carotenoids in agro-food and health in the context of food security, sustainability and health promotion is summarized. Some research needs in relation to Ulva and seaweed carotenoids will be pinpointed.