BLISS is a system programming language developed at Carnegie Mellon University by W. A. Wulf, D. B. Russell, and A. N. Habermann around 1970. It was perhaps the best known systems programming language right up until C made its debut a few years later. Since then, C took off and BLISS faded into obscurity. When C was in its infancy, a few projects within Bell Labs were debating the merits of BLISS vs. C.

BLISS is a typeless block-structured language based on expressions rather than statements, and includes constructs for exception handling, coroutines, and macros. It does not include a goto statement.

The name is variously said to be short for “Basic Language for Implementation of System Software” or “System Software Implementation Language, Backwards”. It was sometimes called “Bill’s Language for Implementing System Software”, after Bill Wulf.

The original Carnegie Mellon compiler was notable for its extensive use of optimizations, and formed the basis of the classic book The Design of an Optimizing Compiler.

DEC developed and maintained BLISS compilers for the PDP-10, PDP-11, DEC Alpha, DEC PRISM, Intel IA-32, Intel IA-64, and VAX, and used it heavily in-house into the 1980s; most of the utility programs for the VMS operating system were written in BLISS-32.