According to Opera Software, the browser had more than 350 million users worldwide (276 million users on mobile) in August 2014. Opera has been noted for originating many features later adopted by other web browsers. A prominent example is Speed Dial.
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 with version 2.0 in 1996, 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 announced it would drop its own Presto 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 rendering engine known as Blink; the same day, Opera confirmed that it would follow Google in implementing Blink.
On 28 May 2013, a beta release of Opera 15 was made available, the first version based on the Chromium project. Many distinctive features of the previous versions were dropped, and Opera Mail was separated into a standalone application derived from Opera 12.
Opera includes built-in tabbed browsing, a bookmarks bar, add-ons, and a download manager. Opera 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.
When the Opera Turbo mode is enabled, Opera compresses requested web pages (but not HTTPS secure pages) by up to 80%, depending upon content, before sending it to the user. This process reduces the total amount of data sent and is particularly useful with slower Internet connections, making pages load faster, or when there are restrictions or costs dependent upon the amount of data transferred. This technique is also used in Opera Mini for mobile telephones  and for smartwatches as well now. 
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. The browser checks the website that is being visited against blacklists for phishing and malware, and displays a warning page if it matches any of these lists.
To catch security flaws and other software bugs before they are exploited or become a serious problem, the Opera Software company maintains a public web form where users can submit bug reports.
In January 2007, Asa Dotzler of the competing Mozilla Corporation accused the Opera Software company 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 present in the previous version of Opera, and thus they would not realize that they needed to upgrade to the latest version or risk being exploited. Opera responded to these accusations the next day.
Opera Software introduced a new release cycle consisting of three "streams" that can be downloaded and installed independently of each other: Opera developer, Opera beta and the Opera final release. New features are first introduced in the developer build, then, depending on user feedback, progress to the beta version and eventually to the official release.
Opera developer 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 enables advanced users to try out new features still under development, without affecting their normal installation of the browser. New versions are released frequently, generally a few times a week.
Opera beta is a feature complete phase, allowing stability and quality to mature before the final release. A new version is released every couple of weeks.
Both versions can be installed alongside the official release without interference. Each has a different icon to help the user distinguish between the variants.
When a user browses the web using Opera Mini, the request is sent via the General Packet Radio Service (GPRS) to one of the Opera Software company's servers, which retrieves the web page, processes it, compresses it, and sends it back to the user's mobile phone.
In addition to the edition of Opera for personal computers, there are versions for a variety of devices.
Opera Mini is a microbrowser designed primarily for mobile phones, but also for smartphones and personal digital assistants. Versions up to 4 used the Java ME platform, requiring the mobile device to be capable of running Java ME applications. The microbrowser began as a pilot project in 2005. After limited releases in Europe, it was officially launched worldwide on 24 January 2006. Opera Mini requests web pages through the Opera Software company's servers, which process and compress them before relaying the pages back to the mobile phone. This compression process reduces data transferred by up to 90% (depending upon content), increasing loading speed, and the pre-processing smooths compatibility with web pages not designed for mobile phones.
Opera browser for Android is a browser for mobile phones and tablets which have the Android operating system. It uses the Blink engine. Opera for Android was released on 21 May 2013. It has the following features:
Combined search and address bar.
Discover feature (a list of websites with the latest news).
Off-Road mode (compression technology to reduce data usage, similar to Opera Turbo).
Opera has had more success in the area of mobile browsing. In 2013, Opera was the third most popular mobile browser worldwide with 16.75% of the market, according to StatCounter. Microsoft will install Opera Software's Internet browser on low and mid-market mobile phones it inherited from Nokia; this could put Opera Mini on another 100 million phones a year. Also, StatCounter showed mobile versions of Opera were the most used in some countries such as Nigeria (64.81%),Belarus (64.47%),Ukraine (58.39%),Russia (42.2%), and Haiti (31.41%).
Versions with Presto 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 engine have been criticized by some users for missing features such as UI customization, and for abandoning Opera Software's own Presto engine. Despite that, versions with Blink 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 interface.