Federal Air Regulation 121.535, addressing the responsibility for operational control of a flight states: The Pilot In Command [(Captain) with the help of his Co-Pilot (First Officer) and for international flights his International Relief Officer (Second Officer)] and the Aircraft Dispatcher (Third Officer) are jointly responsible for the preflight planning, delay, and dispatch release of a flight.

Dispatchers are FAA licensed professionals responsible for planning and monitoring the progress of a flight.  In order to obtain a license, he or she must demonstrate extensive knowledge in meteorology and aviation, to a level that is comparable to that of an airline transport pilot license.  In fact the FAA Airline Transport Pilot License written exam and the FAA Dispatcher written exam are identical. 

The Dispatcher has the authority to delay, divert or cancel a flight at any given time (operational control).  After the release of a flight (in a joint responsibility environment) he uses sophisticated software tools to monitor the flight's progress and advises the flight crew of any circumstances that affect safety.