For example, if your project is to plan the opening of a new store, you may have to create a dependency from your Begin Move-In task to the Final Building Inspection Complete task in someone else's construction project.
To deal with this balancing act, you can create a linked task that represents the timing of the other project (or of a particular task in it). This is also called creating a cross-project link.
Make sure that both the file with the predecessor task and the file with the successor task are open. Identify the filename and task ID (row) number for the predecessor task. Then switch to the file with the successor task and open the Task Information dialog box for the successor task, as just described.
Click in the ID column on a blank row. Type the predecessor filename, a backslash, and then the predecessor task ID number, as in Delta Project/2. Then press Tab to complete the entry. The linked task from the other file appears in the list, as shown here. In the Gantt chart, that external successor appears in gray so you know that it doesn't really "live" in the current schedule file.
You can also insert an entire project and add a link to it so that updates to the other file are reflected in your plan automatically.