A hybrid kernel is a kernel architecture based on combining aspects of microkernel and monolithic kernel architectures used in computer operating systems. The traditional kernel categories are monolithic kernels and microkernels (with nanokernels and exokernels seen as more extreme versions of microkernels). The category is controversial due to the similarity to monolithic kernel; the term has been dismissed by Linus Torvalds as simple marketing.

The idea behind this category is to have a kernel structure similar to a microkernel, but implemented in terms of a monolithic kernel. In contrast to a microkernel, all (or nearly all) operating system services are in kernel space. While there is no performance overhead for message passing and context switching between kernel and user mode, as in monolithic kernels, there are no reliability benefits of having services in user space, as in microkernels.