Infrastructure as a Service (IaaS) in cloud computing refers to a model where a provider offers fundamental IT resources like virtual machines, storage, and networking over the internet, allowing businesses to rent infrastructure instead of buying and maintaining physical hardware; in practice, this means you can spin up servers, configure networks, and scale resources on demand using platforms like Amazon EC2 or Microsoft Azure Virtual Machines, while still having control over the operating system and applications you run. The key difference from PaaS and SaaS lies in the level of control and responsibility—IaaS gives you the most control (you manage OS, runtime, and apps), PaaS abstracts the infrastructure and lets you focus mainly on application development, and SaaS provides fully managed software where everything is handled by the provider. The main benefits of IaaS include flexibility, cost efficiency through pay-as-you-go pricing, scalability, and faster deployment, while common use cases include hosting websites and applications, running development and testing environments, disaster recovery, and handling variable workloads, making it especially useful for businesses that need control over their environment without the overhead of managing physical infrastructure.