The aim of this review article was to present the characteristics and properties of marine algae and their potential applications in agriculture, biofuel production, the food industry, and livestock nutrition. Algae are autotrophic aquatic organisms with a varied morphological structure. The earliest forms of algae evolved in the sea 3.5 billion years ago. These are singlecelled organisms, multicellular and tissue organisms. Brown, red, and green algae have many industrial applications. The algal cytoplasm contains primary and secondary metabolites, minerals, and vitamins which are essential for bodily functions. Algal polysaccharides, in particular alginic acid, fucoidan, agar, carrageenan, carotenoids, chlorophylls, hyaluronic acid, and porphyran, are widely used in medicine, pharmaceutical and cosmetology, and the food industry. Algae can play an important role in sustainable agriculture. They are used in the production of dietary supplements due to their high nutritional value. Algal biomass is a renewable source of valuable bioactive ingredients for food production, and also the chemical sector. The use of algae in livestock nutrition has improved animal performance and the quality of animal-derived raw materials intended for processing. Feed additives containing nutrients and filtered algal suspensions deliver health benefits, thus increasing animal productivity and, consequently, farming profits. Algal species and the optimal harvesting times when seaweed is most abundant in nutrients should be analyzed to minimize the potential adverse effects of algae-based diets of human and animal.