Prior art includes all subject matter (patents, publications, etc.) bearing on the novelty and nonobviousness of a claimed invention pursuant to 35 U.S.C. Sections 102 and 103.  Prior art may include patents, published patent applications, journal articles, textbooks and anything else published and publicly accessible in any language.   Prior art frequently establishes a basis for invalidity of granted patents asserted against a defendant.  

Patent Infringement