The BBC is planning to set up a "digital shop" allowing viewers to pay to download old programmes.
Director-General Mark Thompson said the idea - dubbed Project Barcelona - was the "digital equivalent" of buying a show on DVD.
In a speech to the Royal Television Society in central London tonight, Mr Thompson said the success of the iPlayer - which allows viewers to watch programmes up to seven days after they are first shown - did not change the fact that after a week "a large proportion of what the BBC makes and broadcasts is never seen or heard of again".
He said: "The idea behind Barcelona is simple. It is that, for as much of our content as possible, in addition to the existing iPlayer window, another download-to-own window would open soon after transmission - so that if you wanted to purchase a digital copy of a programme to own and keep, you could pay what would generally be a relatively modest charge for doing so."
Mr Thompson said the idea was "not a second licence-fee by stealth" and other digital download sites would be able to sell BBC programmes.
He said: "The window would be non-exclusive. The BBC would open up one digital shop, but the expectation would be that all this content would also be made available for other existing providers to sell if they wish and that producers could exploit this download-to-own window in any way they wanted."
Mr Thompson said the idea would need the support of programme makers and the BBC Trust, but added it would "mark an important step in broadcast's journey from being a transitory medium into a growing body of outstanding and valuable content which is always available to enjoy and which persists forever."
He also used the speech, at the Cavendish Conference Centre in central London, to talk about his exit from the corporation.
Referring to reports that he will leave the BBC at the end of this year, he said: "Well make of that what you will - I'm not proposing to lay out an exact timetable this evening, I'll share that with the BBC Trust and all of my colleagues at the BBC when the time is right."
But he did hint at leaving before the next BBC charter is renegotiated - which has to happen before December 31 2016.
He said: "I have no idea of what shape the charter debate will take, though I can tell you I'm looking forward to viewing it with 3D specs and a box of popcorn from the stalls."