Glutathione is a sulfur-containing tripeptide composed of glutamic acid, cysteine, and glycine, serving as the major non-protein thiol in many organisms, including plants. It plays a critical role in redox homeostasis, buffering oxidative stress, and influencing protein structure and activity through thiol-disulfide balance. Glutathione acts as a transducer, integrating environmental signals into cellular networks. It is involved in phytohormone signaling and defense against biotic stress. In Arabidopsis, research has begun to identify processes governing glutathione status and its links to signaling pathways. This review discusses glutathione's role in physiological processes such as light signaling, cell death, and defense against pathogens and herbivores. Historically, glutathione was first identified in yeast in 1888, later confirmed in plant and animal tissues. Its structure and biological distribution vary among species, with plants typically accumulating glutathione to millimolar concentrations. Glutathione functions in redox reactions, including the reduction of oxidized forms and the formation of conjugates with electrophiles. It is a key component of the ascorbate-glutathione pathway, which is crucial for hydrogen peroxide metabolism in chloroplasts and stress resistance in plants. Glutathione is measured in plants using various methods, including spectrophotometric assays with DTNB, HPLC with fluorescent derivatization, and in situ techniques like immunolocalization and fluorescent probes. These methods help determine glutathione levels and redox states, providing insights into its role in plant metabolism and defense. Glutathione has multiple functions in plants, including its role in phytochelatin synthesis for heavy metal resistance, sulfur assimilation, and detoxification of formaldehyde. It is also involved in the regulation of sulfur metabolism, with glutathione acting as a reductant for enzymes involved in sulfur assimilation. Glutathione biosynthesis is regulated by enzymes such as γ-ECS and GSH-S, with mutations affecting glutathione levels and plant development. Inhibitors like buthionine sulfoximine (BSO) are used to study glutathione synthesis and its role in plant responses to stress. Overall, glutathione is a multifunctional metabolite in plants, essential for redox homeostasis, signaling, and defense against environmental stresses. Its regulation and synthesis are tightly controlled, reflecting its critical role in plant physiology and development.Glutathione is a sulfur-containing tripeptide composed of glutamic acid, cysteine, and glycine, serving as the major non-protein thiol in many organisms, including plants. It plays a critical role in redox homeostasis, buffering oxidative stress, and influencing protein structure and activity through thiol-disulfide balance. Glutathione acts as a transducer, integrating environmental signals into cellular networks. It is involved in phytohormone signaling and defense against biotic stress. In Arabidopsis, research has begun to identify processes governing glutathione status and its links to signaling pathways. This review discusses glutathione's role in physiological processes such as light signaling, cell death, and defense against pathogens and herbivores. Historically, glutathione was first identified in yeast in 1888, later confirmed in plant and animal tissues. Its structure and biological distribution vary among species, with plants typically accumulating glutathione to millimolar concentrations. Glutathione functions in redox reactions, including the reduction of oxidized forms and the formation of conjugates with electrophiles. It is a key component of the ascorbate-glutathione pathway, which is crucial for hydrogen peroxide metabolism in chloroplasts and stress resistance in plants. Glutathione is measured in plants using various methods, including spectrophotometric assays with DTNB, HPLC with fluorescent derivatization, and in situ techniques like immunolocalization and fluorescent probes. These methods help determine glutathione levels and redox states, providing insights into its role in plant metabolism and defense. Glutathione has multiple functions in plants, including its role in phytochelatin synthesis for heavy metal resistance, sulfur assimilation, and detoxification of formaldehyde. It is also involved in the regulation of sulfur metabolism, with glutathione acting as a reductant for enzymes involved in sulfur assimilation. Glutathione biosynthesis is regulated by enzymes such as γ-ECS and GSH-S, with mutations affecting glutathione levels and plant development. Inhibitors like buthionine sulfoximine (BSO) are used to study glutathione synthesis and its role in plant responses to stress. Overall, glutathione is a multifunctional metabolite in plants, essential for redox homeostasis, signaling, and defense against environmental stresses. Its regulation and synthesis are tightly controlled, reflecting its critical role in plant physiology and development.