[6][7] New feature development for the browser was discontinued in 2016[8] and ended support on June 15, 2022 for Windows 10 Semi-Annual Channel (SAC), in favor of its successor, Microsoft Edge.

Its usage share has since declined with the launches of Firefox (2004) and Google Chrome (2008) and with the growing popularity of mobile operating systems such as Android and iOS that do not support Internet Explorer.

The browser has been scrutinized throughout its development for its use of third-party technology (such as the source code of Spyglass Mosaic, used without royalty in early versions) and security and privacy vulnerabilities, and the United States and the European Union have determined that the integration of Internet Explorer with Windows has been to the detriment of fair browser competition.

[11] The Internet Explorer project was started in the summer of 1994 by Thomas Reardon,[12] who, according to former project lead Ben Slivka,[13] used source code from Spyglass, Inc. Mosaic, which was an early commercial web browser with formal ties to the pioneering National Center for Supercomputing Applications (NCSA) Mosaic browser.

[16][18] Internet Explorer 1.5 was released several months later for Windows NT and added support for basic table rendering.

By including it free of charge with their operating system, they did not have to pay royalties to Spyglass Inc, resulting in a lawsuit and a US$8 million settlement on January 22, 1997.

[28] Internet Explorer 11 was made available for Windows 7 users to download on November 7, 2013, with Automatic Updates in the following weeks.

Microsoft claimed that Internet Explorer 11, running the WebKit SunSpider JavaScript Benchmark, was the fastest browser as of October 15, 2013.

[40][41][42][43] Internet Explorer is still installed in Windows 10 to maintain compatibility with older websites and intranet sites that require ActiveX and other legacy web technologies.

[49] In February 2019, Microsoft Chief of Security Chris Jackson recommended that users stop using Internet Explorer as their default browser.

Users on these versions of Windows 10 were redirected to Microsoft Edge starting on February 14, 2023, and visual references to the browser (such as icons on the taskbar) would have been removed on June 13, 2023.

[63][48] Internet Explorer has been designed to view a broad range of web pages and provide certain features within the operating system, including Microsoft Update.

During the height of the browser wars, Internet Explorer superseded Netscape only when it caught up technologically to support the progressive features of the time.

[69] Internet Explorer has introduced an array of proprietary extensions to many of the standards, including HTML, CSS, and the DOM.

[75] Internet Explorer supports favicons in PNG, static GIF and native Windows icon formats.

Rather, MSHTML.dll exposes an API that permits a programmer to develop a scripting environment to be plugged-in and to access the DOM tree.

[83] Internet Explorer exposes a set of Component Object Model (COM) interfaces that allows add-ons to extend the functionality of the browser.

[81] In addition, web pages can integrate widgets known as ActiveX controls which run on Windows only but have vast potentials to extend the content capabilities; Adobe Flash Player and Microsoft Silverlight are examples.

Starting with Windows Vista, Internet Explorer and its BHOs run with restricted privileges and are isolated from the rest of the system.

In Windows Vista, Internet Explorer by default runs in what is called Protected Mode, where the privileges of the browser itself are severely restricted—it cannot make any system-wide changes.

According to an October 2010 report in The Register, researcher Chris Evans had detected a known security vulnerability which, then dating back to 2008, had not been fixed for at least six hundred days.

[94] Microsoft says that it had known about this vulnerability, but it was of exceptionally low severity as the victim web site must be configured in a peculiar way for this attack to be feasible at all.

[96] In an advisory on January 14, 2010, Microsoft said that attackers targeting Google and other U.S. companies used software that exploits a security hole, which had already been patched, in Internet Explorer.

[105] US-CERT recommended reviewing Microsoft's suggestions to mitigate an attack or using an alternate browser until the bug is fixed.

[106][107] The UK National Computer Emergency Response Team (CERT-UK) published an advisory announcing similar concerns and for users to take the additional step of ensuring their antivirus software is up to date.

[108] Symantec, a cyber security firm, confirmed that "the vulnerability crashes Internet Explorer on Windows XP.

The integration of IE with Windows led to a lawsuit by AOL, Netscape's owner, accusing Microsoft of unfair competition.

The idea of removing a stock install of Internet Explorer from a Windows system was proposed during the United States v. Microsoft Corp. case.

Indeed, programs that depend on libraries installed by IE, including Windows help and support system, fail to function without IE.

It also displayed a fake error message, claiming that the computer was infected with malware and Internet Explorer had entered "Emergency Mode".