Hulu users looking to catch up on past episodes of the likes of "Glee," "House" and other hit shows will have to pay for the service now that the popular video hub has launched a pay service for some of its content.

Hulu Plus is the site's new subscription service that charges users $9.99 per month for access to expanded content -- in high def -- including previous seasons of primetime series. A free version of Hulu is still available but offers only recent episodes of shows from ABC, NBC and Fox.

Access to Hulu Plus is currently by invitation only, with site visitors invited to request an invitation via email to join Hulu Plus during its initial launch phase. The service is being made available across most digital platforms, including the iPhone and iPad, with plans to soon include access via PlayStation 3 and, next year, Xbox.