Both charge and spin density wave condensates couple to electromagnetic fields and the fluctuations of the phase ϕ of the ground states lead to fluctuations of the electric current. The former is appropriate for charge density waves, while the latter is valid for spin density wave transport. The local deformation leads to an internal polarization by virtue of the displaced charge which accompanies the stretched or compressed density wave. The frequency dependent response of spin density waves is expected to be fundamentally different from the frequency dependent conductivity observed in the charge density wave state. The interaction of the collective modes with lattice vibrations and imperfections leads also to damping and therefore to a finite spectral width of the collective mode resonances. The state of affairs is less clear for spin density waves, where major disagreement between theory and experiment remains.