  We study theoretically Electron Paramagentic Resonance (EPR) linewidths for
single crystals of the molecular magnets Fe$_8$ and Mn$_{12}$ as functions of
energy eigenstates $M_s$, frequency, and temperature when a magnetic field
along the easy axis is swept at fixed excitation frequency. This work was
motivated by recent EPR experiments. To calculate the linewidths, we use
density-matrix equations, including dipolar interactions and distributions of
the uniaxial anisotropy parameter $D$ and the Land\'{e} $g$ factor. Our
calculated linewidths agree well with the experimental data. We also examine
the lineshapes of the EPR spectra due to local rotations of the magnetic
anisotropy axes caused by defects in samples. Our preliminary results predict
that this effect leads to asymmetry in the EPR spectra.
