An assay validity for its intended use, as handled in the previous chapter, is critical, but it is just a piece of integral lab quality system without its completion and cohesiveness, lab results do not only lose its value but can be false and misleading. Laboratory quality management system encompasses many aspects and tools that can be bundled into two broad categories: (1) proactive measures to mitigate risk of a system failure and assure the quality of results, which will be produced and (2) retrospective indicators to adjudicate a diagnostic system performance and confirm reliability of the produced results. The first category includes many aspects starting with a lab physical and organizational structures and ending by the tools that assure the integrity of a lab report or a data set, but reagent and equipment verification and instrument calibration are the main analytical tools. The second category includes what is traditionally known as internal (intralab) and external (between-labs) quality control. This chapter will handle the most effective quality tools, challenge current practices, and propose alternatives.