Invite

There are two types of invitations in Guild Wars:
 * 1) Invite to a Party
 * 2) Invite to a Guild

Invite to a Party
Inviting another player to join you is the way to form a party and add to its members. To do this, click on the player's character (or if you can't see him/her hold down 'Ctrl' and click on their name) and then click on the tiny '+' button that will appear next to their name in the Party List window.

To join an existing party, click on any member of the party and invite them. this will be translated into a Request to Join that will be sent to the leader of that party to approve or reject.

Tip: A quick way to invite a member you are interested in off the chat window is to click on their name. This will switch you to the Whisper Channel. Instead of chatting with them, click on their name, then press 'Ctrl+C' (to copy the name) then click in the invite line in your party list and press 'Ctrl+V' (to paste the name) then hit the tiny '+' invite button.

Invite to a Guild
... to be added ...