<!--[if !IE]> not working

Solution 1:

<!--[if !IE]><!--><script src="zepto.min.js"></script><!--<![endif]-->
<!--[if IE]><script src="jquery-1.7.2.min.js"></script><![endif]-->

Note: These conditional comments are no longer supported from IE 10 onwards.

Solution 2:

Browsers other than IE treat the conditional statements as comments because they're enclosed inside comment tags.

<!--[if IE]>
Non-IE browsers ignore this
<![endif]-->

However, when you're targeting a browser that is NOT IE you have to use 2 comments, one before and one after the code. IE will ignore the code between them, whereas other browsers will treat it as normal code. The syntax for targeting non-IE browsers is therefore:

<!--[if !IE]-->
IE ignores this
<!--[endif]-->

Note: These conditional comments are no longer supported from IE 10 onwards.

Solution 3:

An update if somebody still reaches this page, wondering why the ie targeting doesnt work. IE 10 and onward no longer support conditional comments. From the MS official website:

Support for conditional comments has been removed in Internet Explorer 10 standards and quirks modes for improved interoperability and compliance with HTML5.

Please see here for more details: http://msdn.microsoft.com/en-us/library/ie/hh801214(v=vs.85).aspx

If you desperately need to target ie, you can use this jquery code to add a ie class to and then use .ie class in your css to target ie browsers.

if ($.browser.msie) {
 $("html").addClass("ie");
}

Update: $.browser is not available after jQuery 1.9. If you upgrade to jQuery above 1.9 or you already use it, you can include jQuery migration script after jQuery so that it adds missing parts: jQuery Migrate Plugin

Alternatively, please check this thread for possible workarounds: browser.msie error after update to jQuery 1.9.1