Deviation, the occurrence of a non-routine event during manufacture of biopharmaceuticals are a fact of life. Equipment malfunctions, errors by personnel, power interruptions and many other types of unplanned events can impact normal production operations. Good manufacturing practices require that each of these events be catalogued and investigated properly to determine impact to the product, root cause of the event and appropriate measures to correct or prevent issues from recurring. Answering these six questions will allow those responsible to validate the deviation investigation system is effective and compliant.