Abstract: A microfluidic flow controller comprising a substrate having formations defining two or more fluid channels having channel fluid ports which are open at an outer surface of the substrate; and a flexible layer having formations defining a fluid channel which, when the flexible layer is positioned over the substrate so as to cover at least the channel fluid ports, provides a fluid communication path between the channel fluid ports but which, when a force is applied to press the flexible layer towards the substrate, deforms so as to inhibit fluid communication between the channel fluid ports.