Vivaldi (/vɪˈvɑːldi, vəˈv-/) is a Norwegian freeware, cross-platform web browser with a built-in email client developed by Vivaldi Technologies; the company was founded by Tatsuki Tomita and Jon Stephenson von Tetzchner, who was the co-founder and CEO of Opera Software. Vivaldi was initially released on 27 January 2015.

Although it is accessible to general users, Vivaldi's design and feature-set primarily targets power users, in addition to former Opera users disgruntled by its transition from the Presto layout engine to a Chromium-based browser, which resulted in the loss of many of its distinctive features. Even though it is also Chromium-based, Vivaldi aims to revive the features of the Presto-based Opera with its own proprietary modifications.

Vivaldi replaced Firefox as the default browser on the Cinnamon Community Edition of the Manjaro Linux distribution. As of July 2025^[update], Vivaldi claims to have 3.5 million active users.

Vivaldi began as a virtual community website that replaced My Opera, which was shut down by Opera Software in March 2014. Von Tetzchner was angered by this decision because he believed that this community helped make the Opera web browser what it was. Von Tetzchner then launched the Vivaldi Community—a virtual community focused on providing registered users with a discussion forum, blogging service, and numerous other practical web services—to make up for My Opera's closure.

Later, on 27 January 2015, Vivaldi Technologies launched the first technical preview of the Vivaldi web browser. In the first 10 days of being available, Vivaldi was downloaded 500,000 times, which, according to von Tetzchner, was "a very high number, especially if you consider that it's still a technical preview". The browser's name comes from the Italian composer Antonio Vivaldi, which, according to Tatsuki Tomita, is an easy name to be remembered and understood worldwide.

The first stable release of the browser, version 1.0, was released on 6 April 2016. Initially being available only for Linux, macOS, and Windows, Vivaldi was launched with the intent of giving additional functionality when other browsers on the market at the time tried "their best at simplifying, and streamlining their products", according to Ars Technica.

In September 2021, Vivaldi replaced Firefox as the default browser on the Manjaro Cinnamon Community Edition to a mixed reception from the Linux community, as Vivaldi is not "free and open source software"; Manjaro developers cited this decision on Vivaldi's feature-richness and exceptional customisability. In December 2021, Vivaldi became the first web browser to be available for the Android Automotive operating system used in the Swedish electric vehicle manufacturer Polestar's Polestar 2.

Vivaldi has a distinctive user interface with basic icons and fonts, and, optionally, a colour scheme that changes based on the background and design of the web page being visited. The browser also allows users to customise the appearance of UI elements such as background colour, overall theme, address bar and tab positioning, start pages and even its icons and some of its other elements. According to CEO Jon von Tetzchner, Vivaldi's unique customisability is how the browser caters to experienced users.