Modernizr uses feature detection to test the current browser against upcoming features like rgba(), border-radius, CSS Transitions and many more. These are currently being implemented across browsers and with Modernizr you can start using them right now, with an easy way to control the fallbacks for browsers that don’t yet support them.
Lastly, Modernizr also adds support for styling and printing HTML5 elements. This allows you to use more semantic, forward-looking elements such as <section>, <header> and <dialog> without having to worry about them not working in Internet Explorer.
What Modernizr doesn’t do?
Modernizr does not add missing functionality to browsers; instead, it detects native availability of features and offers you a way to maintain a fine level of control over your site regardless of a browser’s capabilities.
Documentation of Modernizr : http://bit.ly/kh5jNW
Source Of The Article: http://www.modernizr.com