Inventors may prepare their own applications and file them in the US Patent and Trademark Office (US PTO) and conduct the proceedings themselves, but unless they are familiar with these matters or study them in detail, they may get into considerable difficulty. While a patent may be obtained in many cases by persons not skilled in this work, there would be no assurance that the patent would adequately protect the particular invention.

Many inventors employ the services of registered Patent Attorneys or Patent Agents. Only US PTO registered Patent Attorneys or Patent Agents are recognized by the US PTO and are permitted by law to represent inventors before the US PTO. The US PTO maintains a register of Attorneys and Agents. To be admitted to this register, a person must comply with the regulations, which require a showing that the person is of good moral character and of good repute and that he has the legal, scientific, and technical qualifications necessary. Some of these qualifications are demonstrated by the passing of a special US PTO examination, known as Patent Bar. Those admitted to the examination must have a college degree in engineering or physical science or equivalent.

The US PTO registers both attorneys at law and persons who are not attorneys at law (Patent Agents). Both Patent Attorneys and Patent Agents are permitted to prepare an application for a patent and conduct patent prosecution in the US PTO. Patent Agents, however, cannot conduct patent litigation in the courts or perform services which constitute practicing law. Patent Agents also cannot provide services related to trademarks. 

In employing a Patent Agent or Patent Attorney, the inventor executes a power of attorney or authorization, which must be filed in the US PTO and is usually a part of the application papers. When a registered Patent Attorney or Agent has been appointed, US PTO does not communicate with the inventor directly but conducts the correspondence with the Patent Attorney or Agent since he is acting on behalf of the inventor.