The Deep Space Network has provided measurements derived from spacecraft radio signals for use in navigation since the dawn of the age of lunar and interplanetary space exploration. In the early 1960s, Doppler measurements made at L-band frequencies provided mrad-level navigation system accuracy. The addition of geographically distributed stations, improvements to ground station instrumentation and frequency standards, transition to higher S-band frequencies, and more sophistication in modeling of spacecraft acceleration and radio wave propagation led to ever-improving system accuracy. With the addition of range measurements in the late 1960s, system performance had improved to the µrad level. Driven by the requirements of increasingly complex missions in the 1970s, dual-frequency S- and X-band downlinks were employed, hydrogen masers were installed, and improved techniques were developed to measure station positions and calibrate the effects of media. The operational use of VLBI in the 1980s led to refinements in the definition of the reference frame, better system calibrations, and direct angular position measurements of spacecraft by the DDOR technique. Navigation system performance improved to the 100-nrad level using DDOR measurements of band-limited telemetry sidebands. Performance improved to the 30-nrad level as wider bandwidth downlinks became available in the 1990s. Continued developments in ground systems, calibration techniques, and modeling sophistication led to improvements in performance to the 5-nrad level by the time of the 2001 Mars Odyssey mission. Even better performance is expected by the middle to end of the decade using Ka-band downlinks.