All-sky data at a number of different wavelengths are used to examine the Giant Radio Loops. The x-ray emission of Loop I is modelled as being due to a Supernova Remnant (SNR) that has evolved in a hot, homogeneous, quasi-isotropic medium. The shock is found to weaken towards higher latitudes, and this is attributed to an increase in the ambient gas temperature away from the galactic plane. Other evolutionary possibilities are examined. Radio spectral index maps from 38 to 1420MHz of the northern celestial hemisphere are produced, and the spectra of loops I and III are modelled on the assumption that the energy distribution of electrons accelerated in the shocks will have an upper energy cut-off due to the finite age of the remnants. It is found that the steepening spectra can be fitted by such a model. The electron distribution below the cut-off of order l0GeV is found to fit best if a flatter spectrum than predicted by simple shock theory is assumed. The idea that shocks. Interacting with clouds can explain this flatter spectrum and enhance the soft x-ray emission is put forward as an alternative evolutionary possibility, bringing together the two separate x-ray and radio emission mechanisms. Other galactic SNR are examined to support this idea, including a newly discovered SNR that exists inside the error circle of the COS-B source 2CG342-02. Although this remnant’s association with the γ-ray source cannot be excluded, no firm evidence is found to identify it as the source.