A microfluidic system and method for its fabrication is disclosed comprising an interposed intermediate layer covering the channel-containing layers, said intermediate layers comprising an integral valve made from the intermediate layer material. A microfluidic system and method is also disclosed for actively pumping a fluid through an integrated layered device incorporating the above-mentioned channels, valves in communication with a chamber, the volume of which can be predictably controlled by interaction between a magnetizable assembly placed on pre-selected sides of the chamber.