<p>There are basically four-and-a-half different systems in place for early applications (with some differences in how each of them is applied):</p>
<ol>
<li><p>Rolling admission. You apply, they consider, they may or may not act on it quickly -- anywhere from a couple of weeks to making you wait until April for a decision. This is mostly used in public universities and colleges. There are no "early" and "regular" applications; they are all regular, whenever filed. However it is commonly believed that standards are a little looser, and scholarships easier to obtain, the earlier one applies.</p></li>
<li><p>Early Action. Early Action colleges say that if you apply by X date (usually November 1) they will give you a yes-no-deferred until April answer by December 15. If you are accepted, you are not committed to enroll. Most Early Action colleges do not mind if you apply to a whole bunch of Early Action colleges early, or even if you apply Early Decision one place and Early Action others. (Georgetown is an exception to that, and there may be others. It does not want you to apply Early Decision somewhere and Early Action to Georgetown. There may be others, and see below. Early Action colleges include MIT, Georgetown, the University of Chicago, Cal Tech, Notre Dame.</p></li>
</ol>
<p>2.5 Single Choice Early Action. This is the deal at Stanford and Yale, and nowhere else. It's the same as Early Action -- apply by date X, hear by date Y (although one of the things you may here is that you are deferred into the "regular" round of decisions), and, most importantly, no commitment to attend if accepted. However, the SCEA colleges do not want you to have any Early Action or Early Decision application in at any other college besides the ONE SCEA college to which you apply. (But rolling admissions applications are treated as non-early applications, so they are OK.)</p>
<ol>
<li><p>Early Decision. Apply by Date X, hear yes-no-deferral by Date Y, but with Early Decision if the college accepts a student by Date Y, the student has agreed in advance to enroll there come hell or high water (or disappointing financial aid package). Because Early Decision may keep a student for shopping for the best scholarship deal, or applying to a dream school, Early Decision colleges get relatively fewer early application, and they tend to accept a much higher percentage of the applications they receive. Almost every private college that doesn't have Early Action has Early Decision, and some state universities, too.</p></li>
<li><p>Nothing. No early application program. This is what Harvard and Princeton, and others, do.</p></li>
</ol>
<p>Usually, a college that offers Early Decision does not also have an Early Action option (except I think Cal Tech may) or rolling admissions, and vice versa.</p>