Fiserv, Inc., is a US provider of financial services technology. The company's clients include banks, thrifts, credit unions, securities broker dealers, leasing and finance companies, and retailers, among others. In October 2015, American Banker and BAI ranked the company third by revenue among technology providers to U.S. banks. Fiserv reported total revenue of $5.51 billion in 2016.

Reorganized in 1984 as a privately held company, Fiserv transformed itself through a corporate acquisitions strategy resulting in more than 150 acquisitions during the following 25 years. Beginning as a $21 million business with 350 employees, by 2009 it had become a Fortune 500 company worth $4.7 billion with more than 19,000 employees.

Fiserv started on July 31, 1984, when Sunshine State Systems, Inc., based in Tampa, Florida, and First Data Processing, based in Milwaukee, Wisconsin, combined to form Fiserv, Inc. Two years later in 1986, Fiserv went public as a $70 million data processor company. Within four years of becoming public, Fiserv was serving a number of large financial institutions in the United States.

In 1991, Fiserv acquired Citicorp Information Resources, a subsidiary of Citicorp. This acquisition put Fiserv into the commercial banking, internal and credit union core account processing market space. Then, in 1995, Fiserv acquired Information Technology, Inc., (ITI), in Lincoln, Nebraska, expanding its number of account processing clients, and gaining, at that time, the most widely implemented account processing platform in the United States, Premier. In 1998, Fiserv reached $1 billion in revenue. Later, in 2007, Fiserv made its largest acquisition to date by acquiring CheckFree Corporation, the leading provider of online banking, online bill payment, electronic bill payment services, and software for check clearance and Automated Clearing House (ACH) processing.

In 2011, the company purchased M-Com, a provider of mobile banking applications; and CashEdge (Popmoney), a provider of electronic funds transfer services. Two years later, the company purchased Open Solutions (DNA). In October 2013, Fiserv announced that it will offer Guardian Analytics products for its clients to secure online banking channels.