The iPhone X (Roman numeral "X" pronounced "ten") is a smartphone that was developed and marketed by Apple. It is part of the 11th generation of the iPhone. Available for pre-order from September 26, 2017, it was released on November 3, 2017. The naming of the iPhone X (skipping the iPhone 9 and iPhone 9 Plus) marked the 10th anniversary of the iPhone.

The iPhone X used a glass and stainless-steel form factor and "bezel-less" design, shrinking the bezels while not having a "chin". It was the first iPhone designed without a home button, a change that became standard on all future models bar two (excluding iPhone SE 2nd and 3rd generations). It was also the first iPhone to use an OLED screen, branded as a Super Retina HD display, one of the best and most advanced displays for its time. The previous Touch ID authentication, incorporated into the former home button design, was replaced with a new type of authentication called Face ID, which uses sensors to scan the user's face to unlock the device. These facial recognition capabilities also enabled emojis to be animated following the user's expression (Animoji). With a bezel-less design, iPhone user interaction changed significantly, using gestures instead of the traditional home button to navigate the operating system. At the time of its November 2017 launch, its price tag of US$999 in the United States also made it the most expensive iPhone ever, with even higher prices internationally.

Along with the iPhone 6s, iPhone 6s Plus and iPhone SE (1st generation), the iPhone X was discontinued on September 12, 2018, following the announcement of the iPhone XS, iPhone XS Max and iPhone XR devices.

The technology behind the iPhone X was in development for five years, starting as far back as 2012. Rumors of a drastic iPhone redesign began circulating around the time of iPhone 7 announcement in the third quarter of 2016, and intensified when a HomePod firmware leak in July 2017 suggested that Apple would shortly release a phone with a nearly bezel-less design, lack of a physical home button, facial recognition, and other new features. A near-final development version of the iOS 11 operating system was also leaked in September 2017, confirming the new design and features.

On August 31, 2017, Apple invited journalists to a September 12 press event, the first public event held at the Steve Jobs Theater on the company's new Apple Park campus in Cupertino, California. The iPhone X was unveiled during that keynote. Its US $999 starting price was the most expensive iPhone launch price ever at the time. The price is even higher in international markets due to currency fluctuations, import fees and sales taxes. An instrumental version of the song Keep On Lovin’ by Magnus The Magnus was used in the reveal of the device, and the song "Best Friend" by Sofi Tukker was featured in the introductory film and ads.

An unlocked version of the phone was made available for purchase in the United States on December 5, 2017.

In April 2018, the Federal Communications Commission divulged images of an unreleased gold-colored iPhone X model. As opposed to the space gray and silver color options that the iPhone X ships with, it was divulged that there were initial plans to release a gold option for the device. However, it was put on hold due to production issues. The successor of the iPhone X, the iPhone XS and iPhone XS Max, included a Gold color option, in addition to the Silver and Space Gray featured on the iPhone X.

Apple released a revised B model for the iPhone X that fixed NFC issues for users in Japan, China, and the United States.