<p>Early admissions is, like munkeegirl said, applying a year early. If anything, it hurts your application because they wonder whether you are mature enough to handle college. </p>
<p>Early action is applying by around Nov. 1 and receiving an early non-binding answer, usually around mid-December. Some schools' EA rates are siginificantly higher than RD (UNC), some are about the same (U Chicago), and some are actually a bit lower (MIT).
For a list:<a href="http://www.usnews.com/usnews/edu/college/rankings/brief/webex/earlyact_brief.php%5B/url%5D">http://www.usnews.com/usnews/edu/college/rankings/brief/webex/earlyact_brief.php</a></p>
<p>Single-choice early action (Harvard, Yale, and Stanford) significantly increases your chances.</p>
<p>Early decision also increases your chances, although ED should not be used as a backdoor into colleges- if you're not willing or able to pay full cost for a college, don't apply ED. You are required to attend that college, and you can't compare financial aid offers.
For a list:<a href="http://www.usnews.com/usnews/edu/college/rankings/brief/webex/earlydec_brief.php%5B/url%5D">http://www.usnews.com/usnews/edu/college/rankings/brief/webex/earlydec_brief.php</a></p>