Content delivery networks (CDNs) enhance web performance by distributing content across multiple servers located globally. By caching content close to users, CDNs reduce latency and improve load times, leading to a better user experience. They mitigate the risk of server overload and ensure high availability during traffic spikes, thereby improving reliability. Additionally, CDNs provide security features like DDoS protection and SSL encryption for enhanced data protection. Overall, CDNs are essential for modern web performance optimization.