In the house the best way is to follow them to find where they come in and then block up the hole. In the garden they are usually harmless unless they make a nest in a pot or right underneath a plant, when the roots can get damaged. But very soon now they will fly on their mating flight, after which most of the males will die and your problems should be over for another year! I don't know how many you have in your garden, but ridding mine of them would be well nigh impossible - but they are only a minor irritation so I leave them alone.

If they are common garden ants and not red ants and not in your house I agree with steragram and leave them alone,but red ants really bite and you wouldn't want these around with little ones.You can buy an ant killer which is in a little tube and you put a little bit (it's a jel) on something quite flat near the nest and they will take it back and this should work.If you are against killing anything then there is a herb you can plant which deters them.I have used this plant successfully but cannot remember the name at the moment.(I know, that was absolutely pointless telling you that!)If i remember I will let you know.

Just found out the name of the herb which deters ants, it is called creeping penny royal.

Ants don't like and will not cross talcum powder! Sorry - I'm only nearly 3 years too late:(!!!