According to both USA cGMP and EU GMP cleanroom classification should be carried out according to ISO 14644-1. The 19994 version of this ISO standard has been re-written by a group of international subject matter experts and ISO 14644-1:2015 was published on December 15, 2015. ISO 14644-1:2015 contains substantial revisions impacting both the way the cleanrooms are classified and the performance requirements of the air particle counting instruments used to carry out the classification.