Here is what we know so far:
- Strikes were launched by British, French and US forces at 2am BST at three sites connected with the Syrian regime's chemical weapons programme.
- The first was at a scientific research centre in greater Damascus involved in the development and production of chemical weapons, the second at a chemical weapons storage facility near Homs, and the third at a chemical equipment storage facility and important command post.
- More than 100 missiles were collectively launched overnight from British, French and American forces in Syria.
- Downing Street has published a document setting out why it says military action against the Syrian regime was legal, stating it has met three conditions permitted under international law.
- During telephone conversations on Saturday afternoon Theresa May, Donald Trump and Emmanuel Macron agreed the military strikes in Syria "had been a success".
- Britain used four Royal Air Force Tornados with Storm Shadow missiles in the air strikes, which they launched from the British RAF base in Akrotiri, Cyprus.
- American Forces deployed B-1B Lancer bombers for last night's strike and used double the number of weapons than in a 2017 missile strike responding to the Khan Shaykhun chemical attack.
- French forces used Mirage and Rafale fighter jets with four frigate warships to launch 12 cruise missiles.
- Theresa May told a press conference in London that joining the bombing campaign with the United States and France was the "right thing for us to do" in the wake of the "harrowing" assault on Douma a week ago.
- UK Labour leader Jeremy Corbyn criticised the British Prime Minister, describing the action as legally questionable. "Bombs won't save lives or bring about peace," Mr Corbyn said.
- US President Donald Trump condemned Syria's two main allies, Russia and Iran, for supporting "murderous dictators".
- French president Emmanuel Macron said "a red line" had been crossed after the chemical weapons attack in Douma.
- US Defence Secretary James Mattis and General Joe Dunford said the strikes were "a one time shot" and that there had been no reports of any allied losses.
- The Russian embassy in the US said it had warned that such actions would "not be left without consequences", adding that insulting President Vladimir Putin was "unacceptable and inadmissible".
- Syrian state TV called the attacks a "blatant violation of international law and shows contempt for international legitimacy".