- Harold Charles Wythes is killed in action in the Second Battle of Bullecourt
- James Budge is killed in action in the Second Battle of Bullecourt
- Federal elections are held in Australia; the incumbent Nationalist Party of Australia led by Prime Minister William ‘Billy’ Hughes defeats the opposition Australian Labor Party led by Frank Tudor by 53 to 22 seats
- The Russian Social Democratic Labour Party – Bolsheviks (RSDLP-B) conference concludes in Petrograd. By an overwhelming majority, the conference adopts Lenin’s resolution on the attitude to the Provisional Government. The Petrograd City Conference of the RSDLP (Bolsheviks)
- The Battle of the Vardar begins in Macedonia; fighting continues until 22 May
Women and children resting on the bank of the River Vardar in Uskub (Skopje), May 1917. Image courtesy Imperial War Museum © IWM (Q 86202).
