XO Group (formerly The Knot Inc.) was an American media and technology company that provided content, tools, products and services for couples who were planning weddings, creating a home, and starting a family. The company generated revenue through online advertising, merchandising, registry services, and publishing. In 2019, the company merged with WeddingWire to become The Knot Worldwide under ownership of WeddingWire's investors. Its divisions remained intact, but the XO Group name has been retired.
David Liu, his wife Carley Roney and their business partners, Rob Fassino, and Michael Wolfson founded The Knot Inc. in 1996. They found that the internet could facilitate and reduce anxiety in the process of wedding planning between couples. The startup received seed financing from AOL, the partners launched The Knot brand as a portal on AOL. In 1997, TheKnot.com launched on the internet.
The company launched an online gift registry in partnership with QVC and published its first book, The Knot Complete Guide to Weddings in the Real World. In December 1999, the company raised $35 million in an initial public offering.
On December 2, 2000, the company launched its own bridal magazine and went public. The Knot Weddings Magazine is published four times a year and is sold on newsstands.
Mike Steib joined XO Group as president in July 2013 and assumed the role of CEO in March 2014.
In October 2015, XO Group announced the acquisition of GigMasters, an online marketplace for event vendors, and a partnership with Jetaport, the discounted hotel room block booking service. 
In September 2018, XO Group announced that it would merge with competing wedding planning firm WeddingWire and become a privately held company under the control of WeddingWire investors Permira Funds and Spectrum Equity.  The merger became official in March 2019 and the new parent company was renamed to The Knot Worldwide.