A new concept of an engine, called a Variable R/L Engine (VR/LE) is presented. The main feature of the engine is the continuous change of the crank-radius to connecting-rod-length ratio. (R/L) during the single engine cycle. The phase shift of the R/L=f(φ), function φ being the crank angle, can be adjusted from outside of the engine and it is a regulational parameter. The variations of the phase angle result in changes of all the engine stroke lengths and also-they are causing the changes of the thermodynamic cycle of the engine. Therefore the phase angle variations make it possible to regulate continuously the compression ratio and the displacement volume of the engine within the range which depends on the engine mechanism geometry. The presented concept can be applied to all the types of the IC piston engines, independently of their size and operation principle.