Early Decision v Early Action

Traditionally, many colleges, particularly ivy league colleges, have accepted up to one-half of their incoming students from their early applicant pool. Because this pool of applicants tends to be significantly smaller, and because the odds of acceptance are greater, applying early can often improve a student's chances of acceptance into his/her college of choice. 

In general, early applicant programs can be divided into two categories: 

Early Decision is usually binding, meaning the student is making a promise to attend, if accepted.  Students seeking this form of early admission are expected to submit an early decision application to only ONE school.  However, this type of decision can present problems for students who need financial aid, as there is little leverage for negotiating.

Early Action is usually non-binding, meaning the student are not obligated to attend the school if accepted.  Students may apply "Early Action" to multiple schools, allowing them to compare offers before making a final decision. How long the student has to decide can vary from school to school.