Picking an Embedded system is a three dimensional problem: size, performance, and features. Together, these characteristics define the embedded space, where your system will reside. On top of these, there are the license and price dimensions which play a vital role in selecting an operating system. Embedded devices have traditionally been isolated, but are now increasingly connected to corporate or public networks for a wide range of applications, forming the Internet of Things. Connecting existing devices that had not been joined before demands an RTOS with the necessary connectivity options in place. This paper presents the challenges and the approaches in selecting an embedded operating system. The approach has been tried in multiple projects and is practically proven.