CSG is a multinational corporation headquartered in Englewood, Colorado. It provides business support systems (BSS) software and services, primarily to the telecommunications industry.

CSG was founded by Neal Hansen as a division of First Data in 1982. It became an independent corporation when it was acquired by CSG Holdings in 1994 for $137 million. A contract with Tele-Communications Inc. (TCI), the largest cable TV business at the time, was influential in the company's growth from $80 million in revenue in 1994 to $171 million by 1997. CSG went public in 1996. A dispute with TCI over pricing led to a $120 million arbitration settlement in 2002 with Comcast, who acquired the TCI business. The two continued to do business together and expanded their relationship in 2014. CSG made more than ten acquisitions in the 2000s, mostly of companies that sold billing, customer service, and operations software.

CSG was founded in 1982 by Neal Hansen under the name Cable Services Group (CSG) as a division of the payment processing company First Data Corporation. At the time, First Data was operated by American Express, which acquired a controlling interest in the company in 1980. CSG became a part of the American Express Information Services Company, which was formed in 1989. The CSG group's first large-scale billing statement processing center, which prints and mails bills to consumers, was established in Omaha in 1990.

Hansen left the Cable Services Group one year after it was founded to become CEO of Applied Communications, where he met George Haddix. Hansen and Haddix formed CSG Holdings with Morgan Stanley and Trident Investment Group in 1994, which acquired Cable Services Group that year for $137 million. In November 1994, Cable Services Group was renamed to CSG Systems International.

CSG was the second largest billing services provider for the US cable television industry by 1994, serving 27 percent of cable TV subscribers. However, according to The International Directory of Company Histories, its profit margins were small and the company was "still in need of a turnaround." Broadcasting & Cable said CSG had lost direction and become complacent. Haddix and Hansen implemented changes at the company, which prompted 350 out of 500 employees to leave the firm within a few months.

The new CSG grew quickly. The convergence of phone, internet, on-demand movies, and other services created more complex billing arrangements between telecommunications companies and consumers, which led to more extensive use of billing services providers like CSG. Professional services and international clients, which were previously not a significant portion of revenues, grew to 22 percent of revenues by the mid-1990s.

In order to pay off debt and raise funding for acquisitions, CSG held an initial public offering in February 1996, which valued the firm at five-fold its original acquisition price. CSG grew from $80 million in annual revenue when it was acquired, to $132.3 million when it went public in 1996 and $171.7 million by 1997.

In the 1990s, Tele-Communications Inc. (TCI) and Time Warner scrapped efforts to create internal billing software and hired CSG International. The 15-year agreement CSG signed with TCI on August 11, 1997 made CSG the largest vendor in the industry and was the primary contributor to its growth in the '90s. By 2001, the deal was responsible for 45 percent of CSG's revenue. As part of the deal, CSG also acquired TCI's internally developed software, SummiTrack, for $106 million. CSG's services to TCI included billing, customer management, and payment processing for TCI customers. In October 1997, CSG International signed its first deal with a utilities company, mc2.