comScore is an American media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers.

ComScore Networks was founded in July 1999 in Reston, Virginia. The company was co-founded by Gian Fulgoni, who was for many years the CEO of market research company Information Resources, Inc. (IRI) and Magid Abraham, who was also an ex-IRI employee and had served as president of IRI in the mid-1990s.

Magid and Gian came up with the idea while working with one of the original investors in the company, Mike Santer, who thought up the concept of creating a very large consumer panel online to track online commerce. The problem was that the traditional methods in which companies were tracking online behavior would not work in tracking commerce, because of the lower incidence of buying online. Normal panels in tracking visitation would be around 20-30K and, with less than 2-3% of the population buying online, the panel size needed to be at least 1-2MM. They decided to build a very large panel using more aggressive recruiting methodology and managing for the error by using advanced statistical methods and controls. Years and tens of millions of dollars went into finding the best ways to measure online buying and other behaviors, plus the level of accuracy required for Fortune 1000 companies to buy.

In 2000, comScore bought certain assets and the customer agreements of PC Data of Reston, Virginia, which was founded by Ann Stephens in 1991. PC Data was among the earliest Web measurement firms, but increasing competitive challenges (including a threat of a patent infringement lawsuit by industry pioneer Media Metrix) put PC Data's future in doubt. The acquisition of PC Data's large customer base helped accelerate the growth of comScore's syndicated measurement service.

By 2001, Media Metrix had built a market share lead but had been unable to create a sustainable financial structure. NetRatings, its closest competitor, was armed with strong capital reserves and announced its intention to acquire and integrate Media Metrix. However, after several months, the FTC announced its intention to block the acquisition and accordingly, NetRatings canceled the transaction. comScore was subsequently able to acquire Media Metrix in a deal announced in June 2002.

Media Metrix originated as PC Meter, a business unit of market research company NPD Group and began publishing statistics in January 1996. In July 1997, it changed its name to Media Metrix, citing the desire to track a wider variety of interactive traffic. In October 1998, Media Metrix merged with its nearest rival, Relevant Knowledge. The company went public as NASDAQ:MMXI in May 1999, reaching a market cap of $135 million on its first day of trading. In June 2000, the company acquired Jupiter Communications for $414 million in stock and changed its name to Jupiter Media Metrix. In the aftermath of the dot-com bubble collapse and associated downturn in internet marketing spending, Jupiter sold the Media Metrix service to rival comScore for $1.5 million in June 2002.

On March 30, 2007, comScore announced its intent to sell shares in an initial public offering and be traded on the Nasdaq using the symbol "SCOR".

In May 2008, comScore announced its acquisition of M:Metrics, a company measuring mobile content consumption. The transaction involved a cash payment of $44.3 million and the issue of approximately 50,000 options to purchase shares of comScore common stock to certain M:Metrics unvested option holders.

comScore announced in October 2009 the acquisition of Certifica, a provider of real-time web measurement and digital marketing technology solutions in Latin America. Based in Santiago, Chile, Certifica has offices throughout Latin America, including Mexico, Brazil, Argentina, Colombia and Peru. The acquisition enhanced comScore’s presence in the rapidly developing Latin American market.

In February 2010, comScore announced it had signed a definitive agreement to acquire the ARSgroup in an all-cash acquisition. Headquartered in Evansville, Indiana, ARSgroup’s areas of expertise included brand strategy, all stages of creative development, campaign evaluation across all marketing and media channels, media planning, return on investment, and forecasting.

On July 1, 2010, comScore announced that it has acquired the products division of Nexius, Inc.

comScore then acquired web analytics and video measurement solutions provider Nedstat (nl) for approximately $36.7 million. Announced on September 1, 2010, the acquisition helps comScore accelerate its global expansion strategy, particularly in European markets.

On February 11, 2014, comScore announced the appointment of Serge Matta as chief executive officer, effective March 1. In February 2015 comScore US entered into a partnership with Kantar owned by WPP with an equity stake purchase.

In September 2015, comScore and Rentrak announced a merger of the two companies. The move was meant to combine comScore's digital media measurement capabilities with the TV measurement capabilities of Rentrak to create a cross-platform media measurement firm, perhaps capable of challenging Nielsen N.V. in the media measurement space. Under terms of the agreement, comScore agreed to acquire Rentrak in an all-stock deal valued at about $732 million, with Rentrak shareholders receiving 1.15 shares of comScore per owned share of Rentrak.

The comScore-Rentrak deal closed on February 1, 2016, with the final transaction being valued at $767.7 million.

Co-founder Gian Fulgoni, who had been serving as chairman emeritus since 2014, abruptly replaced Serge Matta as chief executive officer on August 10, 2016. On September 2, 2016, comScore received a letter from NASDAQ that it was in danger of being delisted from the exchange on September 12 unless comScore filed its 2015 annual report (form 10-K) and reports for the first two quarters of 2016. On Feb 6, 2017, comScore announced they would not meet the NASDAQ-imposed deadline to "complete its financial restatement and regain compliance with Nasdaq's listing requirements." Because of this missed deadline being missed, "comScore's common stock may be suspended from trading and delisted from Nasdaq." If comScore is delisted from NASDAQ and their trading is suspended, they advise they intend to "be quoted on the OTC Markets."

comScore maintains a group of users who have monitoring software (with brands including PermissionResearch, OpinionSquare and VoiceFive Networks) installed on their computers. In exchange for joining the comScore research panels, users are presented with various benefits, including computer security software, Internet data storage, virus scanning and chances to win cash or prizes.

comScore estimates that two million users are part of the monitoring program. However, self-selected populations, no matter how large, may not be representative of the population as a whole. To obtain the most accurate data, comScore adjusts the statistics using weights to make sure that each population segment is adequately represented. To calculate these weights, comScore regularly recruits panelists using random digit dialing and other offline recruiting methods to accurately determine how many users are online, aggregated by geography, income, and age. Correcting the comScore data requires having accurate demographics about the larger pool of users. However, some comScore users are recruited without being asked to give demographic information and, in other cases, users may not be truthful about their demographics. To ensure the accuracy of the data, comScore verifies its users' demographics during the course of measuring statistical data.

The corrected data is used to generate reports on topics ranging from web traffic to video streaming activity and consumer buying power.

With the introduction of Unified Digital Measurement (UDM) in May 2009, comScore implemented a solution to digital audience measurement that organically blended both panel and census-based measurement approaches into a single unified methodology. comScore has developed this proprietary methodology to calculate audience reach in a manner not affected by variables such as cookie deletion and cookie blocking/rejection to help reconcile longstanding differences between the two measurement approaches.

comScore debuted Campaign Essentials in 2010 to measure how digital campaigns are reaching their audiences. In March 2012, comScore launched validated Campaign Essentials (vCE), which introduced the notion of “validated” impressions. In January 2013, comScore announced that it had evaluated 4,000 campaigns for clients covering more than 75 advertising agencies.

In 2006, Ben Edelman, a Harvard researcher, alleged that there were cases where comScore software had been installed on users' computers without their knowledge. comScore admitted that it was in discussion with a spyware firm called DollarRevenue but said that no contract was ever signed, and that once it realized DollarRevenue was distributing comScore's software, months later, it took steps to prevent the DollarRevenue-distributed software from sending data to comScore. Stanford IT notes that the monitoring software has been bundled with file sharing program iMesh without users being aware of it, although comScore's relationship with iMesh was short-lived and occurred several years ago.

In the past, the software forwarded users' internet traffic through comScore proxy servers, provoking criticism about speed performance. As a result, several universities and banks took steps to block the proxy servers. In response to these concerns, comScore no longer uses this technology.

In June 2010, a warning about Mac Spyware being launched from free applications like screensavers, from security company Intego was reported in the media and implicated VoiceFive, Inc. as the source of certain alleged spyware software.

Additionally, noted blogger and angel investor Jason Calacanis claimed that ComScore was running an 'extorting ring' by vastly undercounting publisher traffic numbers and forcing them to pay fees for direct measurement via a tracking pixel. ComScore responded to these allegations by offering their direct measurement tracking pixel to long-tail web publishers for free.

Competitors in internet market research include Alexa, Nielsen Online, Quantcast, SimilarWeb, SRDS by Kantar Media, Thalamus, and Compete, a TNS Media company.

In February 2011, The Coalition for Innovative Media Measurement (CIMM) and comScore announced they were working together to measure three-screen users and their behavior with content and advertising across television, Internet, and mobile.