The Whole Gang's Here

 is a trophy/achievement in Fallout: New Vegas which is awarded for successfully convincing all of the companions to join you.

Possible bugs aside, the eight companions you need for this achievement are: Arcade Gannon, Craig Boone, ED-E, Lily Bowen, Raul Alfonso Tejada, Rex, Rose of Sharon Cassidy, and Veronica Santangelo. .

You must get all the companions in one game in order to get the achievement. There is a youtube video on this,HD Video Guide.

Bugs

 * This achievement is apparently bugged and instead of hiring all of the companions, all you need to do is hire 8 companions; even hiring the same companion (and nobody else) in 8 playthroughs qualifies for this achievement. Editor's Note: This does not work for everyone. See Talk.
 * The achievement may glitch, to where you will not unlock it after you find them all. The easiest way to attempt to fix this is to have them all go to the same place (Lucky 38 suite recommended) and just constantly asking them to follow you, then return to Lucky 38 again.
 * On the PC, despite receiving the achievement, it may not show up in Steam. Achievement was given after dismissing and then rehiring Raul a few times (after hiring all other companions through different games).
 * If you hire Raul but send him to the Lucky 38 multiple times you can end up getting the achievement.