Although national laws may differ somewhat in their definitions, the fundamental requirements for a patent to be granted are that the invention disclosed must be novel and inventive and it must have an industrial applicability.

The invention must be novel: i.e. not included in the 'prior art', which is everything that has been disclosed to the public prior to the date the patent application is filed. In certain non-European countries – such as the USA, Canada, Australia – a patent application is still acceptable if filed within one year of disclosure by the inventor or owner: this is often helpful to academic researchers under pressure to publish research results.

The invention must have 'industrial applicability' – often indicated by whether it may be commercially exploitable. In European and most other countries (the USA is the primary exception), medical methods involving surgery or therapy and diagnostic methods practised on the human or animal body are not patentable. While physicians and veterinarians are free to treat their patients, products (such as pharmaceuticals, surgical and diagnostic equipment) may still be patented.

The invention must be 'inventive': it must possess an inventive step over the closest prior art, and not be obvious to a person skilled in the relevant technology. The legal analysis is frequently controversial: publications describing the technologies closest to the invention are examined for whether they would lead a skilled person to the invention, without using imagination.