Book excerpt: Although observations at the low end of the radio astronomy spectrum were the pre- cursor of all work in radio astronomy, this portion of the spectrum has languished for decades while research at the upper radio frequencies has flourished. Previous work at low frequencies (below 30 MHz) has clearly shown that sensitive high-resolution ground-based observations are extremely difficult to make, if not impossible. Observation quality at low frequencies can leap forward using space-based interferometers. Radio telescopes such as these can be built principally from "off-the-shelf' components. A relatively low cost space program can make great strides in deploying arrays of antennas and receivers that would produce data contributing significantly to our understanding of galaxies and galactic nebulae. This paper discusses the various aspects of low-frequency telescopes such as past history and significant issues like sensitivity, interference, baseline calibration, wave scattering, and mapping. All aspects of the first stages of space-based, low-frequency radio telescopes can be accomplished with no dependencies on new types of hardware. The time has come to open the final electromagnetic frontier in astronomy.