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High energy electron beams with unprecedented intensity and precision are routinely produced at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab). We will discuss the techniques used to deliver spin-polarized beams, and to measure their properties, followed by an exposition of three classes of measurements using these beams. The first measurement helps to define the extent to which quarks account for the proton spin; the second will determine the “neutron skin” in selected nuclei, with applications to the equation of state of neutron matter; and the third is an ambitious attempt to search for physics “beyond the standard model” using a precision measurement of electron-electron scattering.