An LP's legally binding promise to contribute up to a specified amount of capital when called by the GP. The sum of all LP commitments plus the GP commitment equals the fund's committed capital (fund size). Capital is not funded at commitment — the GP issues capital calls (drawdowns) as needed, typically with 10 business days' notice. LPs failing to fund a call are in default and may suffer forfeiture (often 50% of interest), dilution, or forced sale of the interest at a discount. Default is extremely rare among institutional LPs.