Microsoft Azure IaaS:

This is the most basic Microsoft Azure offering, which at bottom gives you a server in the cloud. Opting for that service, you are in full control over the virtual machine, and are responsible for managing everything from the operating system up to the application you are running.

Microsoft Azure PaaS:

This service level also provides an operating system, a database, a web server, an environment for executing your code, and additional services such as identity management. By choosing PaaS for your project needs, Microsoft Azure Cloud Service puts up with all of the tedious operating system details for you, so you can focus all your energy on what really matters to you – developing business applications your customers will love.

Microsoft Azure SaaS:

Level where applications are built and hosted through third-party vendors that usually charge for a certain amount of service – Microsoft Office 365 is one such example. Today, most SaaS applications are built on a cloud platform due to the low cost of entry and the ability to scale up as your customer base grows.