In this chapter the evolution of analogue sampled-data techniques has been reviewed. The switched-capacitor technique has been seen to dominate in general purpose applications, whilst CCDs are being used extensively in imaging arrays. The emergence of mixed-mode analogue and digital signal processing and the subsequent need to integrate analogue sampled-data circuits on a digital VLSI process was identified. It was then seen that switched capacitors are not fully compatible with digital VLSI technology and that advances in technology will degrade their performance. Finally, the use of switched-current circuits, as a digital process compatible analogue sampled data signal processing technique, has been identified and this forms the basis of this text.