What is the project invitation method?

As the Project Administrator, you can allow or restrict participants from inviting an existing Aconex user onto your project.

Setting option Who can invite a new user to your project? How they can issue the invitation
Open Any project participant Use the invite user option to select the Aconex user from the Global Directory. See Invite an Aconex user onto a project. The invited user will be added into your project's directory.
  You You can add the user from the Projects page. See Adding a participant to your project.
Restricted Any project participant Use the invite user option to select the Aconex user from the Global Directory. See Invite an Aconex user onto a project.The invited user will not be visible in your project's directory.
  You You can add the user from the Projects page. See Adding a participant to your project.
Explicit You Only you can add a new user to your project. Add the new user from the Projects page. See Adding a participant to your project. The global directory tab will be hidden for all other users on the project.