This book will cover the reliability of photovoltaic modules. Since PV modules are required to produce electricity for a long time (typically 20 to 30 years) their reliability and durability are key to their commercial success. As PV has now grown into a large industry the reliability is even more critical. Failure of the modules in even one large system could lead to the loss of hundreds of millions of dollars. To understand why PV modules are usually considered a very reliable product, this book will review the history of the reliability efforts showing how field failures were used to develop accelerated stress tests that were then used to provide quick feedback on changes to the products that improved their reliability. Once the reader understands how the industry arrived at its present state, the book will turn to the future, looking at what will be necessary in order to develop a methodology for providing a service life prediction.