Metabolites is an international, peer-reviewed, open access journal of metabolism and metabolomics, published monthly online by MDPI. Open Access — free for readers, with article processing charges (APC) paid by authors or their institutions. Metabolomics within plant science involves the large-scale study of small molecules, also known as metabolites (polar and lipophilic primary metabolites, secondary metabolites, and volatiles), within plant tissues, inclusive of root, stem and leaf tissues, as well as grains/seeds and fruits. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, catalytic activity of their own (usually as a cofactor to an enzyme), defense, and interactions with other organisms (e.g. pigments, odorants, and pheromones). Metabolites are the intermediate products of metabolic reactions catalyzed by various enzymes that naturally occur within cells. Metabolites are small molecules (such as amino acids, lipids, peptides, nucleic acids, carbohydrates, vitamins, and minerals) that are intermediate products of biochemical processes that take place in living organisms. Metabolites are small molecules that supply the cell with energy, structural constituents and the materials to enable the synthesis of other macromolecules such as DNA or proteins. Learn how your body processes THC, why metabolites linger in fat tissue, and how long different drug tests can detect them. Metabolites can be defined as the molecules involved in metabolic pathways, which are linked chemical reactions within cells. They serve as substrates for subsequent reactions and are often categorized into classes such as amino acids, lipids, carbohydrates, nucleotides, and coenzymes. Metabolites represent the end products, intermediates, and starting materials of cellular metabolic pathways, acting as a direct functional readout of the cell’s activity. They include compounds such as sugars, amino acids, lipids, and vitamins, that are constantly cycled through the body’s systems. Living systems are defined not only by their genes or proteins, but by the countless small molecules that constantly flow through cells, tissues, and biofluids. These molecules—collectively known as metabolites—represent the most immediate and dynamic readout of biological activity.