An enrolled agent is a person who has earned the privilege of representing taxpayers before the Internal Revenue Service by passing a three-part comprehensive IRS test covering individual and business tax returns. Enrolled agent status is the highest credential the IRS awards. Individuals who obtain this elite status must adhere to ethical standards and complete 72 hours of continuing education courses every three years.

Enrolled agents, like attorneys and certified public accountants (CPAs), have unlimited practice rights. This means they are unrestricted as to which taxpayers they can represent, what types of tax matters they can handle, and which IRS offices they can represent clients before.
See the IRS website and Circular 230 for more details: http://www.irs.gov/Tax-Professionals/Enrolled-Agents/Enrolled-Agent-Information