Ben Aaronovitch’s Rivers of London series has been optioned by a group called Feel Films. These are the same guys who are adapting Jonathan Strange and Mr Norrell for the BBC.
This is a contract basically where Feel Films has the exclusive right to purchase the rights to the series if they want to. These agreements have a lifespan and if the usual screenplay writing, finding financial backer, sourcing of actors etc doesn’t take place within that time frame, they need to negotiate a new contract or Aaronovitch is free to shop around.
The press release is here.