Ad Extensions give advertisers an opportunity to show something extra about their business in their text adverts.  Ad Extensions help differentiate ads from competing adverts as they help make promotional messages stand out.  They also help boost campaign performance as they have a direct influence on Ad Rank.

They are very easy to set up, will increase CTR when used wisely, increase ad visibility and often cost the same amount as a regular click.

The infographic below (by White Shark Media) covers all the extensions present in the AdWords interface together with valuable tips to make the most of them.  The infographic also made the distinction between manual and automated extensions.