A key early research paper was that of Nancy Kopell and Lou Howard[1] which proved several fundamental results on periodic travelling waves in reaction-diffusion equations. This was followed by significant research activity during the 1970s and early 1980s. There was then a period of inactivity, before interest in periodic travelling waves was renewed by mathematical work on their generation,[11][12] and by their detection in ecology, in spatiotemporal data sets on cyclic populations.[13][14] Since the mid-2000s, research on periodic travelling waves has benefitted from new computational methods for studying their stability and absolute stability.[15][16]