You can assign a title to as many genres as you like. However, you can only have one "main" genre. The main genre is shown in bold in the data entry window.

In this example we have selected four genres ("Action", "Adventure", "Science Fiction" and "Thriller") and "Science Fiction" is the main genre.

When entering data, the first genre you select is automatically set as the main genre. To set another genre as the main genre, right-click and choose "Main Genre" from the popup menu, or simply press Ctrl+Space. To set "Action" as the main genre:

The main genre is available via the Main Genre field. You can group on this field, display it in the browse list, include it in reports, search/filter on this field, etc.

In this example we have grouped by Main Genre and also added it to the browse list. Note that the main genre is highlighted in the explorer pane: