Pyl or PYL may refer to:

• Pyrrolysine, a naturally occurring, genetically coded amino acid
• Jean Vander Pyl (1919–1999), United States actress, she also voiced several cartoon characters
• Pyl Brook, a tributary of Beverley Brook in southwest London, England
• Patriotic Youth League, an Australian Neo-Nazi youth organization that is sometimes abbreviated as "PYL"
• Press Your Luck, a TV Game Show that aired from 1983–1986
• PYL (Korea) is Hyundai Motor Company's marketing project

Pyrrolysine (abbreviated as Pyl or O; encoded by the 'amber' stop codon UAG) is an ɑ-amino acid that is used in the biosynthesis of proteins in some methanogenic archaea and bacterium; it is not present in humans. It contains an α-amino group (which is in the protonated –⁺NH₃ form under biological conditions), a carboxylic acid group (which is in the deprotonated –COO^- form under biological conditions). Its pyrroline side-chain is similar to that of lysine in being basic and positively charged at at neutral pH.