This chapter discusses virtualisation and cloud computing, as they have evolved since the early mainframes up to the present commercial cloud services. Exploring the key role of virtualisation in providing scalable and flexible and multi-tenant environments, it examines core concepts, service models (IaaS, PaaS, SaaS), and deployment strategies (public, private, hybrid and community clouds). Several new trends such as serverless computing, edge/fog, AI-based cloud optimisation, and sustainable cloud computing are discussed, as well as the key cloud companies such as AWS, Microsoft Azure, GCP, IBM Cloud, and Oracle Cloud. Besides introducing real-life applications in the healthcare, government, smart cities, and education sectors, the chapter covers the questions of security, privacy, and governance. With this book, readers obtain the theoretical foundation and practical experience to use cloud computing to innovate and transform digitally.