A key feature of the ILC is that it is a single-pass machine. In contrast to a circular accelerator, where the beam goes around many times, the ILC beams pass through each accelerator element only once, including the interaction point. For the accelerator, this means that for each accelerating module, the machine must be very efficient at transferring wall power into the machine beam, with the added requirement that the final beam must emerge with very low emittance so that it can be focused to the very tiny beam spot required to achieve high luminosity. The ATF-2 at KEK is a special test beam line that has been built to demonstrate the ability to achieve ILC-like namometre beam spots and stabilise them. Recent tests have demonstrated beam spots that are within a factor of two of the ILC design and promise to improve in the future.