Before a medical device can be marketed in the USA a marketing application must be submitted to the FDA and clearance obtained.
Most Class I devices and a few Class II devices are exempt from the requirement for submission of a marketing application. However, these devices are not exempt from other general controls. All medical devices must be manufactured under a quality assurance program, be suitable for the intended use, be adequately packaged and properly labeled, and have establishment registration and device listing forms on file with the FDA. A few Class I devices are additionally exempt from the GMP requirements, with the exception of complaint files and general record keeping requirements. The FDA has a list of exempted devices.
Most Class II devices require Premarket Notification 510(k) (21 CFR 807 Subpart E). A 510(k) is a premarketing submission made to FDA to demonstrate that the device to be marketed is as safe and effective, that is, substantially equivalent (SE), to a legally marketed device that is not subject to premarket approval (PMA). If your device requires the submission of a Premarket Notification 510(k) you can not commercially distribute the device until you receive a letter of substantial equivalence from FDA authorizing you to do so. The FDA site describes the 510(k) or premarket notification in detail. An example is in this link.
On October 26, 2002 the Medical Device User Fee and Modernization Act of 2002 became law. It authorizes FDA to charge a fee for medical device Premarket Notifcation 510(k) reviews. A small business may pay a reduced fee. The FDA website has additional information on medical device user fees, including how to qualify as a small business.
Premarket Approval (PMA) (21 CFR Part 814) is the most stringent type of device marketing application required by FDA. A PMA is an application submitted to FDA to request clearance to market, or to continue marketing of a Class III medical device. The process is more involved and includes the submission of clinical data to support claims made for the device. The FDA describes the Premarket Approval (PMA) in detail.