Abstract: A three-dimensional microfluidic system including: at least one hydrophilic thread along which fluid can be transported through capillary wicking; and at least one hydrophobic substrate for supporting the hydrophilic thread. A method of transporting and mixing a plurality of fluids within a microfluidic system including at least two hydrophilic threads and a hydrophobic substrate having at least two zones, each of the hydrophilic threads supported on a different hydrophobic substrate zone, including: delivering each said fluid to a different hydrophilic thread; and bringing the at least two hydrophilic threads into contact to cause mixing of the fluids.