Revision with unchanged content. With the rapid growth of Internet in scale and complexity, providing quality-of-service (QoS) in Internet becomes increasingly important for network design, traffic engineering, troubleshooting and service-level-agreement (SLA) verification. However, the rapid expansion of Internet makes QoS monitoring a challenging task. The enormous amount of measurement data cause significant increase of cost and resource usage. To solve these problems, sampling techniques are employed in QoS monitoring systems to reduce the measurement complexity and cost. This book provides a comprehensive study of QoS monitoring for SLA verification. Special features include: A focus on the characteristics of QoS metrics as well as major measurement methodologies for monitoring these metrics; an extensive study of widely used sampling techniques; a easy-to-understand theoretical analysis on sampling performance; a detailed description of the proposed adaptive stratified sampling scheme; a particular explanation of the network performance monitoring software design; ample figures, tables and bibliographic references.