Prime Minister David Cameron had argued that Islamic State militants represent a threat to Britain, and his appeal took on greater urgency after the terrorist attacks in Paris.
British forces are already conducting strikes in Iraq. The motion is expected to pass with the support of the ruling Conservative Party. But first, MPs will spend 10 hours swapping fierce rhetoric.
Over 300 hospitals and clinics have been hit with bombs and missiles. Nearly 700 medical workers have been killed. Only Syrian President Bashar Assad has the air power to conduct these attacks.
After immigration officials reverse their decision, five cousins of Alan Kurdi and their parents are planning to move to be with their aunt near Vancouver.
The pledge to bring in 25,000 refugees by year's end was a campaign promise by Canada's new prime minister, Justin Trudeau, helping sweep him to power.
Turkey said the plane violated its airspace and that it had issued 10 warnings before firing. Russian President Vladimir Putin said the downing was a "stab in the back by the terrorists' accomplices."
Both countries oppose the Islamic State. But they have different goals in Syria and have been eyeing each other warily since Russia's military intervened recently.