There are many reasons why adhesive joints fail. Often failure can be related to an extended aging process such as thermal, photolytic, or hydrolytic degradation. These types of failures are due to the service environment and the ability of the adhesive to resist it. Unanticipated catastrophic failures that occur relatively early after production are more troublesome. These are generally related to something unforeseen occurring at the interface that significantly reduces the bond strength of the adhesive. This article reviews the most common factors that are the source of unexpected adhesive failures. Part 2 of the article describes the steps that one might wish to follow when conducting an adhesive failure investigation. The exact cause of adhesive failure is generally difficult to determine because so many factors contribute to bond strength. The following are vital, minimum requirements for all successful adhesive joints, regardless of the type of material or application.