Seaweeds, or marine macro-algae, are known as plants growing on the seashore, in salt marshes, in brackish waters, or in the ocean. Many species of seaweeds have shown an important utilisation for the improvement of plant growth since ancient times, and this positive impact is due to their richness in diverse compounds like lipids, proteins, phyto-hormones, amino acids, antimicrobial compounds and different minerals. Other aspects of various seaweed application had been developed more recently for plant growth and health stimulation: seed germination improvement, shoot and root development, increase in water and nutrient uptake/resistance, phytoremediation and elimination of contaminated soil, and fertilisation. Additionally, the use of marine algae is not limited to agriculture, and it also applies to the pharmaceutical industry (drugs) and other cosmetics. It is well documented that seaweeds are widely used as a source of food in many countries. It is very important to underline that the biotechnological utilisation of seaweeds becomes undeniable in our time, because their richness and diversity can provide humans and animals a continuous food source devoid of pollutants, unlike chemical substances destroying the environment. For this reason, many experiments and reports concerning the diversity, ecology, chemical composition, function and other diverse characteristics of seaweed were carried out, and scientists still continue to investigate the impact this type of aquatic plant has on life on Earth.