Technology-centric products often contain parts, software, and materials that have procurement lives that end before the product they are in reaches the end of its life cycle. Life-cycle mismatches between parts and products, which is referred to as obsolescence, can result in large life-cycle costs for mission, safety, and infrastructure critical products, such as aircraft, medical, and military systems. Diminishing Manufacturing Sources and Materials Shortages is a type of obsolescence that describes the loss of the ability to purchase (or procure) a part (or its associated technology) from its original manufacturer. A key enabler for performing pro-active and strategic management of the life cycle of mission, safety, and infrastructure critical products is the ability to forecast when technologies and parts will become unavailable for purchase, that is, obsolete. This article reviews methods that are used to forecast obsolescence, focusing on long-term forecasting used to predict the obsolescence dates for technologies and electronic parts.