This course focuses on how to design and implement high-performance language VMs for popular managed programming languages such as Python, Java or JavaScript. Throughout the course, all the main components, techniques, and design aspects of a modern language VM will be presented. Most of the topics will be presented in combination with an in-depth analysis of existing open-source language VMs. To this end, the GraalVM Java/Polyglot language VM, and the V8 JavaScript engine will be used as open-source reference implementations. By presenting key concepts in the context of existing open-source projects, the course balances foundational topics on systems internals, their efficient implementation, and practical hands-on experience on real-world software systems.