IDT Corporation (originally standing for International Discount Telecommunications) is an American telecommunications company headquartered in Newark, New Jersey.

IDT was founded by entrepreneur Howard Jonas in August 1990. He founded the company after opening a sales office in Israel, receiving large international phone bills and then discovering a way to lower them by re-originating calls in the United States.

In 1996, IDT founded Net2Phone, the world's fourth-largest VoIP provider (2017), and sold an unnamed share of Net2Phone in August 2000 to AT&T for $1.1 billion in cash.

In November 2004, IDT launched its retail energy business, IDT Energy. As an electric and natural gas supplier, IDT Energy started with customers in New York State. They have entered many more deregulated markets since then including those in New Jersey, Pennsylvania, Maryland, Illinois and Washington DC. In 2014, IDT Energy was awarded the Industry Leadership and Integrity Award at the NYC Energy Marketing Conference.

On January 26, 2006, IDT Telecom, Inc. sold to GVC Networks LLC all its IDT Winstar Solution subsidiaries: Winstar Communications, Winstar Government Solutions, LLC and Winstar Wireless, LLC.

On February 17, 2006, IDT announced it would reacquire full ownership of Net2Phone, a company it had launched in the mid 1990s.

On May 16, 2006, IDT agreed to sell its IDT Entertainment division to Liberty Media "for all of Liberty Media's interests in IDT, $186 million in cash and the assumption of existing indebtedness." On August 31, 2006, the sale of all of IDT Entertainment's US operations and several international operations was completed. "The remainder of the deal, to include the Canadian and Australian operations, is expected to be closed in the next few weeks after regulatory approval has been given." This sale was completed on 29 September 2006.

In March 2006, IDT sold its Russian telecom business, Corbina Telecom, to a Moscow-based consortium of private equity investors for net $129.9 million in cash.

On October 12, 2006, IDT completed the sale of its Toucan consumer phone business in the UK to Pipex for $46.3 million in cash and Pipex stock.

In 2007, IDT acquired a controlling interest in Zedge.net, a social networking community for mobile users and platform for sharing free mobile content.

On September 14, 2009, IDT spun off its CTM Media Holdings to its shareholders. CTM Media Holdings included CTM Media, a distributor of print and online media advertising focused on tourist destinations, and IDW Publishing, a comic book and graphic novel publisher.

On October 31, 2011, IDT spun off its energy related businesses to its shareholders as Genie Energy (NYSE: GNE).

The IDT-owned building at 520 Broad Street in downtown Newark was home to the former Mutual Benefit Life Insurance Company from 1957 to 2000.

Straight Path is a communications asset company, holding 39 GHz (millimeter wave) nationwide spectrum and on average, 800 MHz of bandwidth in top 30 US markets. This spectrum is well suited for next-generation 5G mobile applications.

On April 10, 2017, AT&T entered into an agreement to acquire Straight Path (NYSEMKT : STRP). The offer represented $1.6bn enterprise value and $1.25bn equity value. The all-stock deal was a 162% premium to last close.

After the initial agreement, Verizon and AT&T entered a bidding war which ended with Verizon ultimately buying Straight Path for $3.1bn at a 400% premium

Straight Path was spun off from IDT On July 31, 2013.

In 2009, IDT introduced Boss Revolution, a PIN-less international prepaid calling service. Boss Revolution PIN-less allows smart phone users to make single touch international calls. Since its introduction, Boss Revolution and other PIN-less providers have largely supplanted the traditional prepaid international calling card industry. IDT subsequently announced initiatives to add various payment services to the Boss Revolution Platform, including international money transfer.

IDT inaugurated a service of low cost international calling called PennyTalk. Of note is the use of an Australian actress to play a woman from London during the initial PennyTalk commercial campaign.

Union Telecard Alliance is the distribution arm of IDT Telecom, and one of the largest distributors of prepaid phone cards in the United States with over 200 different phone card brands throughout the country.

IDT operated a wireless MVNO, Tuyo Mobile on the T-Mobile network. It was terminated on May 1, 2012.

IDT spun off Genie Energy to its shareholders on October 31, 2011. It is a holding company comprising several energy-related businesses. IDT Energy, a retail energy provider (an ESCO) serving New York, New Jersey, Maryland, Pennsylvania, Illinois and Genie Oil & Gas, which controls the company's ventures in oil and gas and oil shale research and development in Colorado, Israel, and Mongolia. Despite the name, IDT Energy is fully owned by Genie and no longer belongs to IDT.

Zedge is a mobile content discovery platform and community where users can download content to customize their mobile devices. Zedge was purchased by IDT in December 2006.

Zedge was founded by Kenneth Sundnes, Tom Arnøy, and Paul Shaw in Norway in 2003. Zedge has over 30 million unique visitors per month across web, mobile web, and Android.

Fabrix Systems is an Israel-based software company that developed and licenses a proprietary cloud based, scalable storage and computing platform optimized for media and other big data applications. Fabrix's platform currently powers a Tier 1 US cable operators cloud based DVR offering and is used for cloud based DVR and deep storage by other system operators in North America and Europe.

In February 2015 the company announced it had reached an agreement with Empresa de Telecomunicaciones de Cuba S.A. (ETECSA), Cuba's national telecom provider, for international long distance telephony between the United States and Cuba directly.