In most systems, a patent is the right enforceable in a court, usually to prevent the manufacture, sale and use of a patented invention. It is not, as many people think, permission to practice the patented invention, which may be subject to restrictions for other reasons such as security or public health. Application is made to the court to stop the unauthorized manufacture, sale or use of the invention, so that the court may grant the appropriate order and stop the infringement. In practice, however, the process is less straightforward than it sounds. 

The basis for enforcement of patent rights is established at the start of the patenting process when the patent specification is written by the inventor or the inventor’s patent attorney. 

Having assessed the scope of the patent right, the next task is for the patentee to decide if there is infringement. Before committing himself to the financial risk of a patent case — which can be among the most time-consuming and expensive of all forms of litigation — a patentee must make some attempt to forecast whether he can be successful.   

it is normally considered that a patent which can be shown to be invalid cannot be enforceable. In spite of the examination of patent applications during prosecution, no patent system guarantees the validity of a granted patent. In a patent enforcement action, therefore, a defendant will usually add to any defense of non-infringement a further defense, often in the form of a counterclaim, that the patent is invalid and hence not enforceable even if infringed. 

The task of the court in the determination of infringement is the assessment of the scope of protection defined by the patent and whether the alleged infringement falls within that assessed scope. In the determination of validity, the court (or whatever tribunal is considering validity) should take the same scope of protection as has been defined for the purposes of infringement, and consider whether the evidence produced by the defendant renders the patent invalid with respect to, and to the extent of, the scope of protection claimed by the patentee. 

A company affected by another’s right will carefully assess what its scope is and whether or not it is valid. This highlights a point of particular importance to the owners of patents, namely that claims must be well drafted and properly supported by the disclosure of the invention. They must clearly distinguish the protected subject matter from the prior art and must be neither over- covetous nor too modest. A well drafted patent will often be enough in itself to deter potential infringers. Similar arguments can apply to other rights such as trademarks and designs.