Bootstrap 3 dropped support for Internet Explorer 7, but you can add it back by simply adding this conditional CSS.

<!--[if lt IE 8]>
    <link href="https://raw.githubusercontent.com/coliff/bootstrap-ie7/master//css/bootstrap-ie7.css" rel="stylesheet">
<![endif]-->

• Bootstrap 3 uses the box-sizing property for layouts which is not natively supported by IE7. The polyfill 'boxsizing.htc' is required: https://github.com/Schepp/box-sizing-polyfill

• Glyphicons do not display
• Layout issues (with border-box via the boxsizing.htc polyfill)
• .list-group-item displays incorrectly with bullet points
• Haslayout bug
• .dropdown-menu .divider not displaying
• .sr-only clip syntax
• hr margin top and margin bottom spacing fix

• Percentage width rounding issue Info
• As this is only a CSS stylesheet there may be problems with using Bootstrap 3's JavaScript in IE7.
• Some elements rely on pseudo-selectors which IE7 does not support (first-child, last-child etc)

• Q. Do I need to make any changes to my HTML to add support for bootstrap3-ie7?

  A. Nope! Just include the conditional IE7 stylesheet and you're ready to go!

• Q. Does this include the new Glyphicons introduced in Bootstrap 3.3.2?

  A. Yep!

• Q. What about rounded corners, box shadows and gradients for IE7. How can I get those?

  A. You could use CCS3Pie for adding support for those CSS3 properties to older IE. http://css3pie.com/. If you use that you can add this to your CSS to quickly add border-radius https://gist.github.com/coliff/5618329

• Q. Is the CSS available on a CDN?

  A. Yes, thanks to JSDelivr: https://cdn.jsdelivr.net/gh/coliff/bootstrap-ie7/css/bootstrap-ie7.min.css, however the box sizing polyfill requires the CSS to be hosted locally so the layout will be broken if you serve the CSS from a CDN.

• Q. What about Internet Explorer 6?

  A. Although this CSS does not include IE6-specific fixes, it does fix the webfonts icon, so it's worthwhile using the conditional code if lt IE 8 rather than if IE 7.

• Q. What about Bootstrap 4?

  A. I've created a couple of stylesheets for Internet Explorer 8 and 9 to add support for Bootstrap 4. Check it out at: https://github.com/coliff/bootstrap-ie8

• The boxsizing.htc polyfill can be a little bit buggy. Please make sure you follow the instructions for using that carefully.