hI,

The solution would be to create a project X or Y, and then to consider that these two projects are each one an activity therefore linked by the "interdependencies". ( by the way, which ones?)

You can create dependencies
- from project A to project B
- from project A to activity of B
- from activity of A to activity of B

You just have to have rights on both projects

Here's the "how" part:

Go to the Projects screen. Click on the project you want.
Now scroll down in the bottom half of the screen.
Select the Predecessor element or Successor element section (depends on what you want).
In the table below, click on the green plus sign. A pop-up appears.
Select the type of element (project, activity, meeting, milestone, etc.)
Specify the delay between them, and the type of dependency. Press OK.

This works for the first two options Babynus explained.

To set a "Activity in the current project -> another project" type dependency, select the Planning screen.
In the top half of the screen, select the activity.
The lower half of this screen shows the same Predecessor element and Successor element sections.
Set up your links exactly as explained before.

Thanks NarayanAras for this detailled explanation.

I would just add it is possible to "draw" a dependency in the Gantt chart with Drag & Drop :
- click on predecessor bar,
- hold the button and drag to the successor bar.
A dependency line will be shown in blue, as a proposal.
- Drop (release button) to validate the creation of the dependency.

I considered that, but then we don't have a Gantt chart that shows multiple projects and their tasks.
So IINW this trick is only usable to establish dependency within a project; but it cannot cross the boundary of a project.

You can if :
- both projects are sub-projects of same parent...
- you select all projects (and don't have visibility on too much), close all levels, open only the 2 projects you need...

Yes, of course! Thanks for that clarification!