GCap will embed contextual links to the iTunes store within its online players, playlists and relevant articles across its portfolio of 53 websites.
Radio listeners will be able to download playlist highlights, podcasts and station-recommended albums straight from station-branded areas created within the iTunes Store.
Launch brands include Xfm, Capital 95.8, Choice and Classic FM.
The initiatives will be supported by on-air trails, live DJ mentions, competitions, newsletters and online promotions across the entire GCap portfolio.
GCap and iTunes will collaborate on a number of offers for station listeners. Xfm listeners will be able to register online to receive five free downloads of live material recorded at this year's iTunes Festival:London, while Capital 95.8 will give its listeners the chance to win an iPod Touch and every playlisted track from 2007.
Robin Pembroke, group director of interactive and online at GCap Media, said: "This campaign with iTunes allows our users to easily buy the music they are listening to on our stations. It's another step in developing innovative listening experiences for the computer, iPod and iPhone."