Abstract: Presented is a new rotary or cyclo-valve system for engines, such as internal combustion engines, that greatly simplifies the valve system for such engines. The cyclo-valve simply rotates to align its gas passageways with inlets to or outlets from engine cylinders in time with the combustion and exhaust cycles of the engine. The cyclo-valves themselves may be in the form of a rotary shaft, discs, or similar rotating elements. There are no valve lifters and no valve "float" at high engine rotational speeds as there are with state-of-the-art engines. Gas passageways, while preferred to be through the cyclo-valve, may also pass, at least partially, external to the cyclo-valve. In the preferred embodiment, sealing is at least partially accomplished by labyrinth seals. The instant invention cyclo-valve may be applied to all manner of engine including piston, rotary such as the Wankel, etc.