EPOC16 was an operating system developed by Psion for portable devices, primarily PDAs. Originally it was called simply EPOC. Later it began to be referred to as EPOC16 to distinguish it from the next generation of the operating system: EPOC32, which in turn was known as simply EPOC.

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EPOC was also known as SIBO as it was used in SIBO ("SIxteen Bit Organiser") devices. Specific SIBO devices included the: MC200, MC400, Series 3, Series 3a, Series 3c, Series 3mx, Siena, Workabout and Workabout mx. The MC400 and MC200, the first EPOC16 devices, shipped in 1989.

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All EPOC16 devices featured an 8086-family processor and a 16-bit architecture. EPOC16 was a single-user preemptive multitasking operating system, written in Intel 8086 assembler language and C and designed to be delivered in ROM.