BlackLine is an American enterprise software company that develops cloud-based accounting software that helps businesses manage their quarterly financial reports. The company is headquartered in Los Angeles, California, and has 13 offices globally. BlackLine was ranked number 43 on Forbes Cloud 100 list in October 2016.

In May 2016, a Gartner Magic Quadrant report on the 10 major financial corporate performance management solutions ranked BlackLine among the top four "Leaders" with Oracle, IBM and Workiva.

On October 28, 2016, the company underwent an IPO and listed on the Nasdaq under the symbol BL.

BlackLine was founded in 2001 by Therese Tucker, a former CTO at SunGard Treasury Systems. The company functioned with no outside funding until 2013 when the private equity firm, Silver Lake Partners invested more than $200 million in the company. BlackLine reached an agreement to form a strategic alliance with the financial consulting firm McGladrey, in 2015. As part of the alliance, the companies began offering a business process as a service (BPaaS) solution.

In September 2016, the company acquired its European competitor, Runbook for $34 million. On September 30, 2016, the company filed for an initial public offering with the U.S Securities and Exchange Commission. On October 28, 2016, BlackLine began trading on the Nasdaq market under the BL ticker symbol. In October 2017, BlackLine appointed Tammy Coley as Chief Strategy Officer.

BlackLine provides software for more than 2,000 companies including Costco, Kraft Heinz, Under Armour, Sirius XM Holdings. The company creates enhanced financial controls, in contrast to basic general ledger applications. BlackLine's software manages financial data, reconciles balances from sub-systems, ensures accurate and complete closings, and monitors regulatory controls through a system known as continuous auditing. The company's software is cloud-based, primarily running on the Microsoft cloud stack, and meets ISO 27001 standards.