In a future 'hybrid' mode internal combustion engine capable of running in spark ignition (SI) and controlled auto ignition-CAI (also known as Homogeneous Charge Compression Ignition-HCCI) modes, transition between these modes, during changes in engine load and speed, will play a crucial role. The valve train and engine management system (EMS) must provide a fast and smooth transition between these two very different combustion modes keeping all relevant engine and combustion parameters in an acceptable range. In order to obtain such transition between SI and HCCI and SI, a valve event (duration, timing and lift) has to be variable, which consequently leads to high demands on the valve train and therefore a need for its higher degree of flexibility. Two valve train concepts, one with a Cam Profile Switching (CPS) and phaser system and the other camless using Fully variable Valve Train (FVVT) are presented. The use of both concepts for transitions from SI to HCCI to SI are experimentally investigated on a single cylinder research engine fuelled with commercially available gasoline fuel (95 RON). Experimental results obtained together with benefits and obstacles in using each of these strategies are presented and discussed. Copyright © 2005 SAE International.