From a strategic and an economic point of view, patent prior art searches are very useful for several reasons such as avoiding the infringement of third parties’ rights, reinventing something already new in the state of the art, speeding up the prosecution of a patent application, and getting a patent granted with a lower associated cost. A prior art search is carried out in patent databases (free of charge or fee-based) through keywords or classification symbols, indexing codes (IPC – International Patent Classification or CPC – Cooperative Patent Classification), or a combination of these, using Boolean or proximity operators. The classification codes are independent of the language used and can increase the number of relevant documents retrieved. Patent databases are all incomplete and therefore a search in multiple sources is suggested.