NASA's Mission to Planet Earth attempts to address issues related to environmental change through extensive scientific investigation and global monitoring. As part of this effort, the Earth Observing System Microwave Limb Sounder (EOS-MLS), Joe W. Waters principal investigator, was proposed and is currently in development. The Submillimeter-Wave Radiometer Development group at JPL along with collaborators at the Rutherford Appleton Laboratory in the United Kingdom and a small number of US laboratories are developing space-borne radiometer components to satisfy the detection requirements for EOS-MLS from 200 to 650 GHz with possible extension up to 2.5 THz (119 micrometers ). This conference paper summarizes the development that has been ongoing, with emphasis on the millimeter- and submillimeter-wave mixers. Detailed design and performance data for a subharmonically pumped antiparallel-pair planar-diode mixer are presented including computational simulations and measured mixer noise and conversion loss at 215 and 640 GHz. Results from a modest test program comparing the performance at 215 GHz of planar GaAs antiparallel-pair mixer diodes, planar In53Ga47As devices, GaAs planar-doped-barrier diodes and a GaAs millimeter-wave integrated circuit (MMIC) mixer are also presented. Finally, current and future development efforts in the areas of submillimeter-wave local oscillators, integrated planar-diode mixers, IF amplifiers, and THz radiometers are outlined.