When the Defiance 'Alcatraz' update goes live in the near future, players can participate in a new cooperative feature called "Expeditions". In expeditions, players will face off against ever-increasingly difficult groups of monsters that will require team effort and cooperation to defeat.
To enter an Expedition, players will need to use a Hunter Requisition that can be gained through log in rewards purchased for Bits. Once spent, players will be placed into the appropriate Expedition based on EGO rating. The higher one's EGO rating, the higher the tier of difficulty will be. Tier difficulty determines how hard monsters are to defeat, but also determines the quality of gear that can be acquired.
Players can complete an expedition, return to Alcatraz to purchase new gear and head right back in to continue the climb up the tiers for even better quality gear.
Read more about Expeditions, including a fairly comprehensive list of monsters players will encounter, on the Defiance site.