A multi-TeV electron-positron collider, such as CLIC, is one of the most attractive options for the future of accelerator-based high energy physics. This seminar will briefly, and in simple terms, point out the motivation for building such a collider. The emphasis of the talk will be on the conceptual design of the detectors, needed to perform measurements at CLIC with the required accuracy. Some of the technological challenges will be explained in detail, using a few key examples.