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During 2016–2017 novel strains of highly pathogenic H5 avian influenza virus within the Goose/Guangdong/96 (Gs/GD/96)-lineage (mainly H5N8) caused multiple outbreaks of disease in poultry and wild birds across much of Europe, parts of Asia, the Middle East and West Africa, and have extended for the first time to affect poultry in Eastern and Southern Africa. The virus was reported first in the Tyva Republic in late May 2016 before being detected elsewhere. This was the fourth intercontinental wave of transmission by an H5 virus within this lineage and was by far the most severe in terms of the number of countries affected. Observations from earlier intercontinental outbreaks of Gs/GD/96-lineage H5 HPAI from 2005 onwards may help forecast the probable course of this current panzootic,1 although it also demonstrates that the behaviour of H5 HPAI viruses in this and previous waves has varied. If the reasons for these differences can be determined, (viral, host and environmental factors), it may help improve forecasting and hence preparedness and early detection of viral incursions. In particular, the detection of a novel virus in wild birds on the Tibetan plateau and surrounding areas largely devoid of commercial poultry production, (including northern Mongolia and southern Russian Federation), in May-June of any year is likely to be followed later that year by detection of a similar virus in other distant countries, extending into Europe, South Asia and Africa. Evidence from earlier waves also suggests that the current virus could return to Europe in 2017–2018, although the number of outbreaks is expected to be lower than in 2016–2017. In the current fourth intercontinental wave, the virus has been detected in a range of farm types, intensive and extensive, with a higher proportion in domestic ducks, geese and turkeys, but chickens have also been affected. Secondary spread between poultry farms appears to have occurred in at least six European countries: Hungary, France, Bulgaria, Germany, Poland and the United Kingdom, (APHA, 2017), but many appear to be primary cases not directly related to other cases on poultry farms. At about same time as the H5N8 virus appeared in Europe an H5N6 subtype virus also within the Goose/Guangdong/96-lineage caused a massive outbreak of disease in layer chickens and ducks in the Republic of Korea. This virus has not been detected there since early April 2017. Movement of both viruses has been associated with infection in wild birds and their role in the long distance transmission of these viruses during the autumn migration is now irrefutable.