C is an imperative (procedural) systems implementation language. It was designed to be compiled using a relatively straightforward compiler, to provide low-level access to memory, to provide language constructs that map efficiently to machine instructions, and to require minimal run-time support. C was therefore useful for many applications that had formerly been coded in assembly language.

Despite its low-level capabilities, the language was designed to encourage machine-independent programming. A standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with little or no change to its source code, while approaching highest performance. The language has become available on a very wide range of platforms, from embedded microcontrollers to supercomputers.

C is designed to provide high-level abstracts for all the native features of a general-purpose CPU, while at the same time allowing modularization, structure, and code re-use. Features specific to a particular program's function (features that are not general to all platforms) are not included in the language or library definitions. However any such specific functions are implementable and accessible as external reusable libraries, in order to encourage module dissemination and re-use. C is somewhat strongly typed (emitting warnings or errors) but allows programmers to override types in the interests of flexibility, simplicity or performance; while being natural and well-defined in its interpretation of type overrides.

C's design is tied to its intended use as a portable systems implementation language. Consequently, it does not require run-time checks for conditions that would never occur in correct programs, it provides simple, direct access to any addressable object (for example, memory-mapped device control registers), and its source-code expressions can be translated in a straightforward manner to primitive machine operations in the executable code. Some early C compilers were comfortably implemented (as a few distinct passes communicating via intermediate files) on PDP-11 processors having only 16 address bits; however, C99 assumes a 512 KB minimum compilation platform.