Crew Resource Management. It’s a concept that is relatively new to the aviation scene. The idea behind CRM is that work flows and communication in the cockpit and with the rest of the crew is optimized.
A lot of aviation accidents in the past were due to a lack of CRM. The most famous would probably have to be the Tenerife Disaster, the most fatal aircraft accident in history (583 died) (dont say September 11 attacks trumps this, it wasn’t an accident!).
Many factors were at play. However the captains refusal to listen to the first officers comments about not being cleared for take-off where probably the main cause of the accident. CRM is aimed at getting the entire crew to work together. The attitude of “do what the captain says” is no longer accepted.
Imagine modern day CRM looked something like this clip from The High and the Mighty:
That clip was stolen from here.
UPDATE: Check out this page from Wikipedia to learn more about CRM.