Dynamic ads typically enable the specific content of an ad - words, images, offer etc - to change based on conditions and rules. For example, if a customer has purchased from your website they may receive a different message than a non-website visitor. Or a supermarket may want to promote a different product based on say location of the ad viewer, or based on a third-party variable like weather. This list of ad providers all provide tools which enable you to set up campaigns which can change ad content based on such variables. The list is prioritised by the level of creative control provided.