Well, the season, nor the series, are currently available in their entirety, but you can now stream the entire twelfth and final season of The Big Bang Theory on CBS All Access.
The show’s twelfth season consists of 24 episodes, with episodes 23 and 24 being part of the series finale, which your standard 45-60-minute long finale to wrap up the series.
Other than that, there is no other way to stream the season (legally) at this time, as CBS and CBS All Access have a streaming monopoly for that show at this time.
To watch older episodes and seasons of the series, your best bet is to check your cable, satellite or live TV streaming service’s on-demand options, as a well as the TBS app. The TBS app will enable you to stream older episodes of the series, but only if you are signed in with your cable, satellite or live TV streaming service credentials.
CBS All Access is available in the CBS app that is available on the iPhone, iPod Touch, iPad, Apple TV and Mac.