What caused this latest rejection of Sinn Fein's involvement in government?
The Good Friday agreement - which established the Northern Ireland executive - allowed for Sinn Fein's inclusion as long as they pursued republican objectives solely by peaceful, democratic means. But last week police raided Sinn Fein's Stormont offices, and addresses at other locations in Belfast, on suspicions that an IRA spy ring was operating within the party. Among those arrested was Denis Donaldson, a former IRA prisoner and currently Sinn Fein's head of administration.
Sinn Fein angrily denounced the police raid as a politically motivated attack on the Good Friday agreement.
What happens now?
The Northern Ireland office will take over the assembly's departments. Mr Reid will take over Mr Trimble's position as first minister. Two other Labour MPs have been drafted in from Westminster to help run the assembly's 10 government departments.
The 20 pieces of legislation currently under consideration in Belfast will either have to be put on hold until the assembly reconvenes, or will be passed by council, or by Westminster.
How long will suspension last?
Mr Reid set no firm date for the reintroduction of devolved rule and governments in both London and Dublin fear suspension may continue until next spring, or even later. Mr Reid announced that he hoped elections in Northern Ireland would go ahead as planned in May next year.
What happens to the members of the assembly?
Mr Trimble and the Social Democratic and Labour party deputy first minister, Mark Durkan, will lose their £108,000 a year pay, and other ministers will lose £75,000. Assembly members - now on £41,000 - could have their pay cut to £29,000, but that is up to Mr Reid.
Has the assembly been suspended before?
Yes, three times in less than three years. In February 2000, former Northern Ireland secretary Peter Mandelson suspended the assembly after a lack of IRA disarmament prompted a crisis. After the IRA announced in May that it would put weapons beyond use, the assembly was restored.
Last year, Mr Reid announced two one day suspensions after Mr Trimble resigned over the IRA's failure to follow through on the earlier promise to put weapons beyond use. The first suspension took place on August 10, allowing six more weeks to resolve the crisis. The second suspension on September 21 did the trick. On October 23, an impartial, international body verifies that the IRA has - for the first time - put weapons beyond use.
Where does this leave the Good Friday agreement?
In trouble. If the allegations against Sinn Fein are proven, and party members at Stormont were spying for the IRA, it is hard to see how the assembly could continue in its present form.