How do I search for photos that aren't in a project

In Aperture, every Image must be in a Project. The set of Images that are not in Projects is null by design; perforce there is no way to search for these items that do not exist.

For a short review of the parts of Aperture and how they inter-relate, click.

Try using the search bar on the upper right under the viewer menu and the loupe button.

I'm doing some more organising of my photos that aren't in any projects.

iPhoto and Aperture are using the word "Project" for different kinda of library items. Perhaps your question is misunderstanding because of this inconsistency.

• Aperture's "OProjects" correspond to the "Events" in iPhoto and not to iPhoto's "Projects".
• And iPhoto's "projects" (books, cards, calendars) are called "Products" in Aperture.

What Kirby explained for Aperture's projects is also true for events in iPhoto. Every image is in exactly one Aperture project or iPhoto event.

I can search for photo's that aren't in an album.

If you want to search in Aperture for images, that have not been used in any album, you can do that with a smart album or a search rule:

• Use "File > New > Smart Album".
• Set the source in the smart settings to "Library".
• Add an Aperture Meta Data rule from the "Add Rule" drop-down menu.
• Set the rule to "Album name is empty".