Article 9 reduces the whole of secured lending to three questions asked in a fixed order, and almost every loss a secured lender suffers comes from answering one of them carelessly. This article works through attachment, perfection, and priority in sequence, explaining what value, rights in the collateral, and an authenticated security agreement actually require, why a collateral description that works in a financing statement may be fatally inadequate in a security agreement, and how the five perfection methods map onto collateral types. It then takes up the details that generate real litigation: the debtor name rules and the search-logic safe harbor, the choice-of-law rule keyed to debtor location, continued perfection after a move or merger, proceeds, and the twenty-day purchase money grace period with its separate and unforgiving inventory notification requirement. Part four works the priority ladder, including why control beats everything in a deposit account and why the buyer in ordinary course takes free of a perfected interest the buyer knows about. Part five covers enforcement and the rebuttable presumption rule that punishes a sloppy foreclosure sale, and part six covers what happens when the debtor files bankruptcy, where the trustee's strong-arm power converts an unperfected interest into no interest at all.