This review provides a comprehensive and systematic study of plant biostimulants, focusing on the fundamental and innovative principles underlying this technology. The authors emphasize the need to define the biological basis of biostimulant function to develop a science-based industry and regulations. They propose a definition of biostimulants as "formulated products of biological origin that improve plant productivity through novel or emergent properties of their complex constituents, rather than solely due to known essential nutrients, plant growth regulators, or protective compounds." The review highlights the complexity of biostimulants, which can be derived from various sources such as bacteria, fungi, seaweeds, higher plants, animals, and humate-containing raw materials. The authors discuss the challenges in determining the mode of action for biostimulants and suggest that research should focus on proof of efficacy and safety, without requiring a specific mode of action. They also emphasize the importance of integrating multiple methodologies, including omics technologies, to advance the field. The review covers the history of biostimulants, their classification, primary sources of raw materials, production technologies, and bioactive components, providing a comprehensive overview of the current state and future directions of biostimulant science.This review provides a comprehensive and systematic study of plant biostimulants, focusing on the fundamental and innovative principles underlying this technology. The authors emphasize the need to define the biological basis of biostimulant function to develop a science-based industry and regulations. They propose a definition of biostimulants as "formulated products of biological origin that improve plant productivity through novel or emergent properties of their complex constituents, rather than solely due to known essential nutrients, plant growth regulators, or protective compounds." The review highlights the complexity of biostimulants, which can be derived from various sources such as bacteria, fungi, seaweeds, higher plants, animals, and humate-containing raw materials. The authors discuss the challenges in determining the mode of action for biostimulants and suggest that research should focus on proof of efficacy and safety, without requiring a specific mode of action. They also emphasize the importance of integrating multiple methodologies, including omics technologies, to advance the field. The review covers the history of biostimulants, their classification, primary sources of raw materials, production technologies, and bioactive components, providing a comprehensive overview of the current state and future directions of biostimulant science.