Freedom to Operate (FTO) (also known as Right to Use, or Clearance search), includes a comprehensive Infringement search of unexpired US patents. These searches also include a limited validity search of expired and unexpired patents, publications, and non patent literature. These searches also help to locate expired patents and provide relevant proof of an invention that is already in public domain.

One of the primary tasks of Freedom to Operate searches, therefore, is to determine if the innovation has freedom to operate in any particular country. That is why, it is vital to maintain patent databases and use the latest patent tools to make the searches.

Below are some reasons why the matter claimed in the patent could still be obtainable:

• Similar patents may still be available in other countries. You can always use the claimed matter in countries where no related patents have been issued.
• Laws about patentability vary from country to country. So even if a patent application was made, it need not have been approved.
• Some of the patents may have lapsed due to defaulting on due payments.
• Patents have limited shelf life, so it makes sense to verify the expiration dates.
• Generally, a particular patent claim can be rendered invalid due to the existence of some kind of prior art, like a publication or a presentation, about the matter claimed in the patent, that the patent examination process missed. In fact, a patent can be challenged in some countries just because an inventor wasn't correctly named.