Patents can protect technical inventions for a maximum period of 20 years. Put simply, an invention is technical if the inventor is typically expected to be an engineer or a natural scientist. Accordingly, a game or business idea, a business concept or a linguistic algorithm for speech recognition are not inventions that are eligible for patent protection.

In order to be protected by a patent, an invention must also be new and based on inventive step, i.e. it must be sufficiently far removed from the prior art. Prior art includes everything that has been made accessible to the public by written or oral description, by use or in any other way before the filing date. The relevant state of the art is determined by the patent offices and held against the applicant, as far as it is relevant for the assessment of protectability.

After grant, a patent effective in Germany can be attacked by third parties by filing an opposition within nine months after grant. After expiry of the opposition period, nullity action can be brought before the Federal Patent Court. Many foreign legal systems provide for comparable possibilities of attack on patents.