What are ACID properties in MySQL?

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ACID defines the four properties a relational database must guarantee for transactions to be reliable. MySQL with the InnoDB engine is fully ACID-compliant. Atomicity — all statements in a transaction succeed or none do; ROLLBACK undoes partial work. Consistency — transactions move the DB from one valid state to another; constraints, foreign keys, triggers all enforced. Isolation — concurrent transactions don't interfere; controlled by isolation levels (READ UNCOMMITTED, READ COMMITTED, REPEATABLE READ, SERIALIZABLE). Durability — once committed, data survives crashes; InnoDB uses redo logs and fsync. Know all four: Atomicity (all or nothing), Consistency (valid state), Isolation (no interference), Durability (permanent after commit). The bank transfer example demonstrates atomicity. Know the four isolation levels and MySQL's default (REPEATABLE READ). SAVEPOINT for partial rollback is an advanced detail.