HBTU (O-(Benzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate) is a widely used peptide coupling reagent known for its high efficiency and speed in forming amide bonds, particularly in solid-phase peptide synthesis (SPPS). It activates carboxylic acids to form highly reactive intermediates with low racemization rates, making it suitable for synthesizing complex peptides. Compared to older reagents like DCC, HBTU avoids the formation of insoluble urea byproducts, simplifying purification. It is also more reactive and efficient than EDC, especially in non-aqueous systems. While it shares similarities with HATU, HBTU is generally considered less toxic and more cost-effective, offering a good balance between performance, stability, and accessibility, which has made it a go-to reagent in both academic and industrial peptide synthesis labs.