The purpose of this lecture is to introduce to the audience the basic ideas of quantum limited amplifiers, SQUIDs and SETs. These devices operate by utilizing fundamental quantum phenomena, which is beautiful and interesting in its own right. This has been harnessed to construct the most sensitive amplifiers known, close to the quantum uncertainty principle. Here I will describe some of the applications of these devices which varies from the position sensor on a multi-ton gravitational wave detector, to measuring the temperature of a nanostructure.