ACI Worldwide Inc. is an American payment systems company headquartered in Elkhorn, Omaha, Nebraska.

[3] ACI develops a broad line of software focused on facilitating real-time electronic payments.

ACI Worldwide's products and services are used globally by banks, financial intermediaries such as third-party electronic payment processors, payment associations, switch interchanges, merchants, corporations, and a wide range of transaction-generating endpoints, including automated teller machines ("ATM"), merchant point of sale ("POS") terminals, bank branches, mobile phones, tablet computers, corporations, and internet commerce sites.

[5][citation needed] BASE24 was expanded over time to service transactions from other channels, such as POS terminals and bank branch systems.

The product portfolio grew to cover functions related to card transactions, such as clearing, settlement and fraud detection.