The US Patent and Trademark Office (PTO) has established a certification process that involves taking an examination (the Patent Agent's Exam) after having obtained an approved college degree in engineering or science. Both attorneys (i.e. people that have completed a law degree and have passed the bar examination in a state) and nonattorneys may take the exam as long as they have a college degree in engineering or science that meets the PTO requirements. A Patent Attorney is a lawyer with adequate technical background (i.e. in possession of a college degree in engineering or physical sciences) that has passed the USPTO Patent Exam in addition to the bar examination in a given state. On the other hand, a Patent Agent is a nonattorney with adequate engineering/scientific preparation that has passed the USPTO Exam. Patent Agents can prepare patent applications on behalf of inventors, file patent applications, respond to USPTO office actions (i.e. letters), and participate in the amendment of the applications. In summary, a Patent Agent is a licensed professional certified by the USPTO to prepare and prosecute patent applications. The difference between a Patent Agent and a Patent Attorney is that a Patent Agent cannot advise the inventors regarding the legal consequences that may arise from ownership of the IP. For instance, it cannot provide legal advise regarding how the ownership rights may be affected in the case of a divorce, for the purposes of making a will, or regarding the terms of a licensing contract. These legal issues outside the scope of patent law require the professional counsel of an attorney.

Information regarding the USPTO Patent Exam can be found at http://www.uspto.gov/go/dcom/gcounsel/oed.htm. Briefly, this site includes information regarding the requirements for registration, examples of past exams, and result statistics. Current examinations are based on the 8th Edition (Rev. 2) of the Manual of Patent Examining Procedure (MPEP). The passing rate in the last exam was 58.2%. There are many firms that offer training services, educational programs, and self-study materials for the Patent Bar Exam.


References:
[1] Stim, R. "Intellectual Property. Patents, Trademarks, and Copyrights" West Legal Studies.
[2] Black's Law Dictionary 5th ed., (West Publishing, 1979).
[3] Manual of Patent Examining Procedure, 8th Edition