Tryptophan (English: Tryptophan, an abbreviation Trp or W) is one of the 22 standard amino acids, essential amino acids the body can not synthesize, so it must draw from food. Its standard genetic code, codon for UGG, only the L- stereoisomer or tryptophan have tectonic activity of proteins, R- stereoisomer is occasionally found in naturally occurring peptides. Tryptophan obvious structural formula characterized in that it contains indole functional group. It is a serotonin (also known as "serotonin") precursor, serotonin is important neurotransmitter. Tryptophan is most dietary proteins or protein-containing foods in a conventional ingredients.

It is particularly rich in chocolate, oats, dried dates, milk, yogurt, cheese, red meat, eggs, fish, poultry, sesame, chickpeas, sunflower seeds, pumpkin seeds, spirulina, bananas and peanuts.
Turkey contains a particularly high amount of tryptophan. Tryptophan significant presence in almost all forms of plant proteins, some are also very rich. Tryptophan may affect brain serotonin synthesis, psychology, when purified form to be administered orally, for research alter serotonin concentrations. Due to the lack of tryptophan-induced protein drug technology to produce low brain serotonin, known as "acute tryptophan depletion." Using this method studies to assess the impact of serotonin on emotions and social behavior, and found to reduce aggression and serotonin increase agreeableness.
Tryptophan is an important intrinsic fluorescent probe (amino acids), which can be used to estimate the properties of tryptophan microenvironment. Most of the folded protein intrinsic fluorescence emission is due to excitation of tryptophan residues.