MicroCSP is a run-time system written in C supporting process-oriented concurrency. It features CSP-style synchronous communication over point-to-point channels and alternation (including timeouts) and implements preemptive priority process scheduling. The MicroCSP programmer writes the logic of a process as an ordinary function which, barring preemption, runs to completion every time the process is scheduled. To make such an approach feasible requires that the programmer cast each process's logic in normal form: a loop controlling a single choice of guarded events, with event-free computation following each event. A context switch requires a mere function call, with the exception of those that occur as the result of an interrupt. The system is memory-efficient, fast and has a narrow hardware interface. The intended target of MicroCSP is bare microcontroller hardware, and its efficient use of the stack makes it particularly suitable for microcontrollers with restricted memory. The current version runs on a single processor over a Linux implementation of the hardware interface and serves as a prototype for the microcontroller implementations. A multicore implementation appears to be possible.