The article "Building Scalable Web Sites" discusses techniques for creating websites that can handle large numbers of visitors without slowing down. The author, Cal Henderson, explains how to build sites that can keep users happy even when there are thousands or millions of them. The book covers strategies for back-end scaling, architecture, and failover to ensure websites can handle countless requests. It also explores ways to integrate with other services like email, SOAP, RSS, and Ajax-based web applications. The goal is to help advanced developers improve the performance and cost-effectiveness of their web applications.