Microsoft Internet Explorer, abbreviated IE or MSIE, is a proprietary graphical web browser made by Microsoft and currently available as part of Microsoft Windows. Internet Explorer is the most widely used web browser today, although since 2004 it has lost some usage share to other browsers. As of October 2005, IE's usage share is about 85% (see the market adoption section).

Internet Explorer is an integrated component of all current versions of Microsoft Windows. Microsoft has shipped Internet Explorer as the default browser in all versions of Microsoft Windows since Windows 95 OSR1. The last major upgrade to Internet Explorer was included in Windows XP Service Pack 2, but is not available for older versions of Windows. The beta version of Internet Explorer 7 for Windows XP SP2 has been available since July 27, 2005.

Internet Explorer had also been available as a separate, free-of-charge product for many older versions of Windows, and several other operating systems: for some time, Microsoft produced Internet Explorer for Mac and Internet Explorer for UNIX (the latter for use through the X Window System on Solaris and HP-UX). All of these versions have ceased active development, although Internet Explorer for Mac will still be available for download from Microsoft until January 31, 2006.

Internet Explorer is now known as Microsoft Internet Explorer, but the name will be slightly changed to Windows Internet Explorer in Windows Vista.