Every player in New World: Aeternum is a member of a Company, even if they are the only member of their own. Players can join each other's Companies, which allows them to work together to achieve things they couldn't alone.
To invite someone to your Company, use the flyout on their <a action="GoToPage" data="Mechanics_SocialMenu">Player Portrait</a>. To join someone else's Company, you will need to be invited in the same way. Once you've received an invitation, you can accept it from the <a action="GoToPage" data="Mechanics_SocialMenu">Social Menu</a>.
You do not need to leave your Company before joining another. You will be removed from your previous Company automatically.
All claimed <a action="GoToPage" data="Companies_Territories">Territories</a> and player-built <a action="GoToPage" data="Companies_Building">Structures</a> are owned by Companies, and can be used by any member with adequate <a action="GoToPage" data="Companies_Ranks">permissions</a>. This means that any Territory you claim or Structure you build is to the benefit of your Company and all its members. Conversely, leaving a Company means you lose access to those Structures since it's the Company that owns them, not the player.
Companies will also want to capture and defend Territories. They usually do this through <a action="GoToPage" data="Companies_War">War</a>, which allows them to fight each other without the usual <a action="GoToPage" data="Mechanics_Crime">criminal penalties</a>. Wars also include a Siege phase, during which the Defender's Territories' protection can be bypassed.
Companies have Treasuries that the Governor and Consuls can withdraw from. Any member of the Company can provide money to this Treasury, making it easy to collect funds for Company use, like buying <a action="GoToPage" data="Companies_Territories">Claim Charters</a>.
Up to 50 players can be in a single Company. Players cannot be members of multiple Companies at once.