Microwave radiation spans a range of wavelengths that can be produced by very cold astronomical sources, or by warm sources like protoplanetary disks and clouds of interstellar molecules. Microwave telescopes must be able to act somewhat like infrared telescopes and somewhat like radio telescopes. They therefore are built and operated using a fascinating blend of technologies. Depending on the scientific goals, they can be put in space, in high-altitude balloons, or on the ground at mountaintop observatories. Some of the detectors used include bolometers and heterodyne receivers.