MPs have voted to allow military action to be carried out in Syria.
A big debate and vote was held in the House of Commons in Westminster on Wednesday.
MPs were deciding whether RAF planes should be allowed to carry out airstrikes in Syria against the group that calls themselves the Islamic State.
The vote ended 397 in favour of sending planes to Syria and 223 against.
The group called IS has carried out attacks all round the world - most recently in the French capital Paris.
British warplanes are already attacking them in Iraq but Prime Minister David Cameron told MPs that Britain should bomb them in the country next door, Syria, as well.
RAF Tornado jets carried out Britain's first air strikes against IS in Syria after the vote was taken.