The US Pharmacopeia (USP), the Japanese Pharmacopoeia, and the European Pharmacopoeia "Microbial Limits Tests" are in the final stages of harmonization. The harmonized USP chapters are slated for implementation in 2009. This article describes the harmonized USP Chapters <61> "Microbial Enumeration," <62> "Absence of Specified Microorganisms," and <1111> "Microbiological Attributes of Nonsterile Pharmaceutical Products," and suggests they will likely require some revalidation of existing methodologies. Companies should put plans in place immediately for this work and show consistent progress towards this goal.