Dear Nanite it is a good point which I did not realize that spatial dispersion describes one specific sort of nonlocal behaviour that exists in homogeneous infinite media only In fact spatial dispersion is relatively common in optics one example being Doppler broadening in gases but it can often be approximated by frequency dispersion As a result I believe SD gets less attention than it would deserve in E M courses When one holds a hammer all problems look like a nail when a generation of physicists is taught the local theory almost everybody tries to describe metamaterials in terms of local parameters This however causes much confusion because as far as I know above GHz range we are only able to make metamaterials that are spatially dispersive and lossy If no fundamental breakthrough comes I guess it will remain true in the next decades I therefore happily support the idea of writing a robust and readable article on spatial dispersion though I can not promise to invest much time in it now The article can in general relate to any waves propagating in a nonlocal homogeneous medium so the theory can be composed of wave equation and convolution with nonlocal response function The second part of the article could focus on the electromagnetic wave extending the subject to the electromagnetic L L 103 106 theory and mentioning several examples including gases and metamaterials What do you think about this