Micro- and macroalgae have garnered considerable scholarly interest as sustainable and multifunctional resources for the formulation of enhanced nutritional supplements. These aquatic organisms, encompassing microscopic phytoplankton and extensive seaweeds, are abundant in bioactive compounds, which include polysaccharides, proteins, essential fatty acids, minerals, and vitamins. Microalgae, exemplified by Chlorella and Spirulina, are acclaimed for their elevated protein concentrations and antioxidant pigments, whereas macroalgae, comprising red, green, and brown seaweeds, are distinguished for their polysaccharides such as carrageenan and fucoidan, which demonstrate prebiotic and immunomodulatory attributes. This chapter investigates the nutritional compositions of both micro- and macroalgae, accentuating their health-related advantages, including antioxidant activity, support for cardiovascular health, modulation of the gut microbiome, and anti-inflammatory properties. The escalating interest in algal-derived supplements has prompted significant advancements in cultivation and processing technologies, thereby facilitating the production of products characterized by high quality and bioavailability. Nevertheless, obstacles such as scalability, palatability, safety, and adherence to regulatory frameworks continue to pose challenges. Effectively addressing these issues is imperative for realizing the full potential of algae as a sustainable resource for functional foods and dietary supplements. This chapter offers a thorough examination of current applications, the global market landscape, and prospective research trajectories, emphasizing the transformative impact of algae in fostering health and well-being through sustainable practices.