Portland cement concrete has low environmental impact, versatility, durability, and economy, which make it the most abundant construction material in the world. This article details the types and causes of concrete degradation. Concrete can be degraded by corrosion of reinforcing steel and other embedded metals, chlorides, carbonation, galvanic corrosion, chemical attack, alkali-aggregate reaction, abrasion, erosion, and cavitation as well as many other factors. The article addresses the durability of concrete by two approaches, namely, the prescriptive approach and the performance approach. In the former, designers specify materials, proportions, and construction methods based on fundamental principles and practices that exhibit satisfactory performance. In the latter, designers identify functional requirements such as strength, durability, and volume changes and rely on concrete producers and contractors to develop concrete mixtures to meet those requirements.