The year of a fund's first capital call (or sometimes first close) — the most important organizing variable for performance benchmarking. Funds of the same vintage deploy into similar market conditions, compete for similar opportunities, and exit into similar markets, so cross-vintage comparison is meaningless; within-vintage quartile rankings are the standard benchmark. Typical U.S. buyout vintage benchmarks (2000-2015): top-quartile IRR 18-30%, median 10-17%, bottom-quartile 3-10% — a top-to-bottom spread of 1,000-1,500 bps that makes manager selection the central LP task.