The difference is reversibility.<p>ACH never settles, it just hasn&#x27;t returned yet. There&#x27;s a 60 day window for ordinary not authed returns, and even past that in cases of fraud.  ACH is also push or pull, you can push money or the person you&#x27;re paying can pull. (Or paychecks. A lot of paychecks are run over ACH). There are limits on ACH, depending on what you&#x27;re doing its anywhere from 2.5k to 25k to $10^8.<p>Wires are nearly irreversible.  Once you send the money, it&#x27;s Gone.  So the banks have a lot more documentation that they do for retail customers.  Wires are push only.