Opera began in 1994 as a research project at Telenor, the largest Norwegian telecommunications company. In 1995, it branched out into a separate company named Opera SoftwareASA. Opera was first released publicly in 1996 with version 2.0, which only ran on Microsoft Windows. In an attempt to capitalize on the emerging market for Internet-connected handheld devices, a project to port Opera to mobile device platforms was started in 1998. Opera 4.0, released in 2000, included a new cross-platform core that facilitated creation of editions of Opera for multiple operating systems and platforms.
Up to this point, Opera was trialware and had to be purchased after the trial period ended. Version 5.0 (released in 2000) saw the end of this requirement. Instead, Opera became ad-sponsored, displaying advertisements to users who had not paid for it. Later versions of Opera gave the user the choice of seeing banner ads or targeted text advertisements from Google. With version 8.5 (released in 2005) the advertisements were removed entirely and primary financial support for the browser came through revenue from Google (which is by contract Opera's default search engine).
Among the new features introduced in version 9.1 (released in 2006) was fraud protection using technology from GeoTrust, a digital certificate provider, and PhishTank, an organization that tracks known phishing web sites. This feature was further improved and expanded in version 9.5, when GeoTrust was replaced with Netcraft, and malware protection from Haute Secure was added.
On 12 February 2013, Opera Software announced that it would drop its own Presto layout engine in favour of WebKit as implemented by Google's Chrome browser, using code from the Chromium project. Opera Software also planned to contribute code to WebKit. On 3 April 2013, Google announced that it would fork components from WebKit to form a new layout engine known as Blink; the same day, Opera Software confirmed that it would follow Google in implementing Blink layout engine.
On 28 May 2013, a beta release of Opera 15 was made available, the first version based on the Chromium project. Many distinctive Opera features of the previous versions were dropped, and Opera Mail was separated into a standalone application derived from Opera 12.
In July 2016, the Opera browser was sold to Qihoo for $600 million. On 4 November 2016 Golden Brick Capital (Qihoo included) completed the acquisition.
In January 2017 the source code of Opera 12.15 (the last version that was still based on Presto layout engine) was leaked.
Opera includes built-in tabbed browsing, a bookmarks bar, add-ons, and a download manager. Opera also has "Speed Dial", which allows the user to add an unlimited number of pages shown in thumbnail form in a page displayed when a new tab is opened. Speed Dial allows the user to more easily navigate to the selected web pages.
Opera Software claims that when the Opera Turbo mode is enabled, the compression servers compresses requested web pages (excepts HTTPS pages) by up to 50%, depending on the content, before sending them to the users. This process reduces the amount of data transferred and is particularly useful for crowded or slow network connections, making web pages load faster or when there are costs dependent for the total amount of data usage. This technique is also used in Opera Mini for mobile devices and smartwatches.
One security feature is the option to delete private data, such as HTTP cookies, browsing history, items in cache and passwords with the click of a button. This lets users erase personal data after browsing from a shared computer.
When visiting a site, Opera displays a security badge in the address bar which shows details about the website, including security certificates. Opera also implements a proprietary protocol from Google called "Safe Browsing" to check the website that is being visited against blacklists for phishing and malware, and displays a warning page if it matches any of these lists.
In January 2007, Asa Dotzler of the competing Mozilla Corporation accused Opera Software of downplaying information about security vulnerabilities in Opera, (that were fixed in December 2006). Dotzler claimed that users were not clearly informed of security vulnerabilities that were present in the previous version of Opera, and thus they would not realize that they needed to upgrade to the latest version or else risk being exploited by hackers. Opera Software responded to these accusations the next day.
In 2016 free VPN support was implemented in the browser. Opera said that this would allow encrypted access to Web sites otherwise blocked, and provide security on public WiFi networks. Either VPN or Turbo mode can be supported, but not both.
Opera Software uses a release cycle consisting of three "streams" (which correspond to phases of development) that can be downloaded and installed independently of each other: "developer", "beta" and "stable". New features are first introduced in the developer build, then, depending on user feedback, it progress to the beta version and eventually released.
The developer stream allows early testing of new features, mainly targeting developers, extension creators, and early adopters. Opera developer is not intended for everyday browsing as it is unstable and is prone to failure or crashing, but it enables advanced users to try out new features that are still under development, without affecting their normal installation of the browser. New versions of the browser are released and frequently, generally a few times a week.
The beta stream, formerly known as "Opera Next", is a feature complete package, allowing stability and quality to mature before the final release. A new version is released every couple of weeks.
Both streams can be installed alongside the official release without interference. Each has a different icon to help the user distinguish between the variants.
Desktop web browser market share according to StatCounter for September 2016.
In 2015, Opera was the fifth most popular desktop browser worldwide, according to StatCounter. In Q3 2016, Opera's usage share across all platforms was 5.67%.
Opera was the fifth most popular browser for mobile phones worldwide in 2015 with 11.00% of the market, according to StatCounter. Opera Mini will become the default web browser for Microsoft’s existing feature phone and Asha product lines that Microsoft acquired from Nokia; this could put Opera Mini on another 100 million phones a year. Opera is the most popular browser for mobile telephones in most African countries and in several Asian countries.
Versions with Presto layout engine have been positively reviewed, although they have been criticized for website compatibility issues. Because of this issue, Opera 8.01 and higher had included workarounds to help certain popular but problematic web sites display properly.
Versions with Blink layout engine have been criticized by some users for missing features such as UI customization, and for abandoning Opera Software's own Presto layout engine. Despite that, versions with Blink layout engine have been praised for being fast and stable, for handling the latest web standards and for having a better website compatibility and a modern-style user interface.