The review summarizes and systematizesthe data accumulated in recent years as a result of research and commercial trials of seaweed extracts (SE). The results of the assessment of SE as a special class of biostimulants and the key problems of the manufacturing process of SE biostimulants are presented. The chemical composition of SE and a range of their positive effects on plants, such as accelerating seed germination and rooting of cuttings, stimulating the growth of shoots and roots, increasing the efficiency of nutrient uptake and plant yield are described. Evidence is given for the ability of SE to alleviate plant stress caused by various abiotic or biotic factors. Possible involved mechanisms at metabolic and genetic level are discussed. Examples of the influence of SE on plant rhizosphere are considered. The priority tasks are stated, the solution of which should determine the prospects for the use of SE in agriculture in the coming years.