Seaweeds are an important natural source of highly valuable bioactive compounds, namely vitamins, proteins, essential amino acids, omega-3 polyunsaturated fatty acids, essential minerals and trace elements, carotenoids, polyphenols, enzymes and carbohydrates. Their bioactive compounds have been associated to several biological activities, such as antioxidant, anticancer, antidiabetic, antimicrobial, anticoagulant, antiviral, antiinflammatory, immunomodulatory, prebiotic, and hypocholesterolemic. Due to their richness in highly valuable compounds and well-balanced composition, seaweeds have become a promising and innovative source of new functional ingredients, that can be used in the development of novel food products as well as nutraceuticals, and thus, improving human health, well-being, and quality of life, and also contributing in the prevention and treatment of diseases. This review provides an overview of the knowledge acquired in the last years about seaweeds and the health benefits associated with their bioactive molecules, as well as their consumption and the development of seaweed-based functional foods and nutraceuticals.