Seaweed extracts are considered biostimulants that promote plant growth and development. Marine algal seaweeds are underutilized bioresources with a long history of use as food, industrial materials, and in therapeutic and botanical applications. They are also used as amendments in crop production systems due to their plant growth-stimulating compounds. However, the biostimulatory potential of these products has not been fully explored due to limited scientific data on growth factors and their mechanisms of action. This review provides a comprehensive overview of the effects of various seaweed species and products on plant growth and development, emphasizing their use in sustainable agricultural systems. Seaweeds are integral to marine coastal ecosystems and include macroalgae classified into three main groups based on pigmentation: Phaeophyta (brown), Rhodophyta (red), and Chlorophyta (green). Brown seaweeds are the second most abundant group, with about 2,000 species, commonly used in agriculture. Seaweed products have been used for centuries as soil conditioners due to their organic matter and fertilizer nutrients. Approximately 15 million metric tonnes of seaweed products are produced annually, with many used as nutrient supplements and biostimulants to enhance plant growth and yield. Numerous studies have shown beneficial effects of seaweed extract applications on plants, including improved seed germination, crop performance, resistance to stress, and postharvest shelf-life. Seaweed products exhibit growth-stimulating activities and are used as biostimulants in crop production. Biostimulants are materials that promote plant growth when applied in small quantities. Seaweed components such as macro- and microelements, amino acids, vitamins, cytokinins, auxins, and abscisic acid-like substances affect cellular metabolism, leading to enhanced growth and yield. Seaweed extracts are bioactive at low concentrations, and their chemical components may exhibit synergistic activity. Seaweeds, especially red and brown algae, are sources of complex polysaccharides, minerals, and trace elements that affect plant growth.Seaweed extracts are considered biostimulants that promote plant growth and development. Marine algal seaweeds are underutilized bioresources with a long history of use as food, industrial materials, and in therapeutic and botanical applications. They are also used as amendments in crop production systems due to their plant growth-stimulating compounds. However, the biostimulatory potential of these products has not been fully explored due to limited scientific data on growth factors and their mechanisms of action. This review provides a comprehensive overview of the effects of various seaweed species and products on plant growth and development, emphasizing their use in sustainable agricultural systems. Seaweeds are integral to marine coastal ecosystems and include macroalgae classified into three main groups based on pigmentation: Phaeophyta (brown), Rhodophyta (red), and Chlorophyta (green). Brown seaweeds are the second most abundant group, with about 2,000 species, commonly used in agriculture. Seaweed products have been used for centuries as soil conditioners due to their organic matter and fertilizer nutrients. Approximately 15 million metric tonnes of seaweed products are produced annually, with many used as nutrient supplements and biostimulants to enhance plant growth and yield. Numerous studies have shown beneficial effects of seaweed extract applications on plants, including improved seed germination, crop performance, resistance to stress, and postharvest shelf-life. Seaweed products exhibit growth-stimulating activities and are used as biostimulants in crop production. Biostimulants are materials that promote plant growth when applied in small quantities. Seaweed components such as macro- and microelements, amino acids, vitamins, cytokinins, auxins, and abscisic acid-like substances affect cellular metabolism, leading to enhanced growth and yield. Seaweed extracts are bioactive at low concentrations, and their chemical components may exhibit synergistic activity. Seaweeds, especially red and brown algae, are sources of complex polysaccharides, minerals, and trace elements that affect plant growth.