While synchrotron emission in supernova remnants has been observed and analyzed to great effect at radio wavelengths, there is a growing number of both galactic and extragalactic supernova remnants with nonthermal (non-plerionic) emission in the X-ray band. In the past the only tool available to describe X-ray synchrotron emission was the generic powerlaw model. Powerlaw models are inadequate on several levels. I will present synchrotron models, which use the radio spectral index and flux as inputs and include the full single-particle emissivity. Models of synchrotron emission can account for the spectra of dominantly nonthermal supernova remnants with interesting consequences for residual thermal abundances and acceleration of particles to cosmic ray energies. In addition, these models, which use the radio spectral index and flux as inputs, deliver a much better-constrained separation between the thermal and nonthermal components. These models make both spectral and spatial predictions, describing how the nonthermal emission varies across the remnant. The integrated spectrum of SN1006, a remnant dominated by nonthermal emission, is well described by synchrotron models. Armed with spatially resolved nonthermal models and new thermal models we now have the tools to separate thermal and nonthermal X-rays in supernova remnants - a capability as essential to understanding the thermal component, as it is to study the nonthermal emission.