An embedded operating system is an operating system for embedded computer systems. Embedded operating systems are computer systems designed to increase functionality and reliability for achieving a specific task. Resource efficiency comes at the cost of losing some functionality or granularity that larger computer operating systems provide, including functions that may not be used by the specialized applications run. Depending on the method used for multitasking, this type of OS is frequently considered a real-time operating system or RTOS. Embedded systems are mostly used as Real-time operating systems.

All embedded systems contain a processor and software. There must be a place for embedded software to store the executable code and temporary storage for run-time data manipulations. These take the form of ROM and RAM, respectively. All embedded systems must also contain some form of inputs and outputs to function. Within the exception of these few common features, the rest of the embedded hardware is usually unique and varies from application to application. The hardware running an embedded operating system can be very limited in resources; therefore the embedded design of these operating systems may have a narrow scope tailored to a specific application to achieve the desired operation under these constraints. The embedded operating system that organizes and controls the hardware usually determines the rest of the embedded hardware needed.

To take better advantage of the processing power of the CPU, software developers may write critical code directly in assembly. This machine efficient language can potentially result in gains in speed and determinism at the cost of portability and maintainability. Often, embedded operating systems are written entirely in more portable languages, like C, however.

An important difference between most embedded operating systems and desktop operating systems is that the application, including the operating system, is usually statically linked into a single executable image. Unlike a desktop operating system, the embedded operating system does not load and execute many applications. This means that the system is only able to run a few application(s).