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Compton scattering provides a fast and accurate measurement of the longitudinal polarization of electron beams available at linear colliders. At the SLC, green (532 nm) circularly polarized light from an Nd:YAG laser, frequency doubled, collides nearly head-on with electrons after they have passed the e+e-interaction point but before they have encountered any dipole bending magnets.Unique to this application, the recoil electrons, rather than scattered photons, are detected, after being momentum analyzed by the bending magnets nearest to the interaction point. Thus we achieve spatial separation of several centimeters between electrons from scattering at different Compton angles.The analyzing power of Compton scattering of 2.34 eV photons from 45.6 GeV electrons is 75% at full backward scamring. The analyzing power is zero at 90 degrees in the electron rest frame, and data from this channel helps us correct for luminosity variations in the electron-photon collisions.The Compton polarimeter is capable of measuring the electron beam polarization to within a few percent of itself. Statistical accuracy of better than 1% in the absolute beam polarization is achieved routinely in runs of three minutes duration, with the laser firing at 11 Hz. Figure 1 shows the Compton Light Source and the Compton Electron Detectors in relation to the e+e-Interaction Point within the SLD detector, and to the nearest bending magnet in the south final focus region of the SLAC Linear Collider. (preserves circular Back Scanered e-

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