Sequential extraction of zero-coupon discount factors P(0,T_i) from market instruments of increasing maturity (deposits, FRAs/futures, then par swaps), each step solving for the unknown P(0,T_i) given par-pricing of the next instrument. Post-2008, single-curve bootstrapping was replaced by multi-curve: an OIS (now SOFR-OIS) discount curve plus separate forecasting curves per tenor basis (1M, 3M, 6M), because tenor-basis spreads ceased being zero. Cubic-spline or monotone-convex interpolation between nodes; the choice meaningfully affects forward rates.