The iTunes Affiliate Programme allows media and content owners to link to the iTunes Store from any of their digital communications (websites, apps, emails, social media platforms etc) and to claim a 7% commission from any of the resulting sales within a 24 hour purchase window.
The Affiliate Programme is used by content owners (e.g. record labels, app developers, movie studios, artists, actors) as a great customer experience in their marketing. It is also used by media owners (e.g. radio stations, online newspapers and magazine, portals, bloggers, recommendation engines) to create an incremental revenue stream by providing contextual links to purchase the content that they review or feature or to fill unsold advertising inventory.
To get started, you can apply here.