2 or 3 parties of adventurers can form one party called an alliance. All members of an alliance can attack the same enemies. It is mainly used to defeat very strong enemies that can't be defeated by one party of 6 adventurers.
Minimum: 2 parties with 2 people (2 party leaders).
Maximum: 3 parties with 18 people.
Note: You can not make yourself party leader solo, so the minimum can only be achieved by forming and disbanding.
Forming the Alliance
To form an alliance you need 2 parties. As party leader search for the other party leader with the search function and press form in the menu instead of invite. You are now the alliance leader. To invite a third party to the alliance you need to repeat the same procedure with the third party leader. Only the alliance leader can invite the third party.
Normally it is possible to invite new members into your party if they are in the same region as you. However, in order to invite a party into your alliance, that party's leader must be in the same area as you.
You may pass the alliance leadership to a party member.
You may pass the alliance leadership to another party leader in the alliance using "/acmd leader <playername>"
Skills and Magic
Spells and Skills which work only on party members like Erase still can only be targeted within the specific party.
Alliances are not very useful for gaining Experience Points outside of Abyssea Zones.
Alliances can work together for Experience Points in Abyssea.