moving library aperture

The Aperture Library is a package and not a file. In the Finder, drag it to the external, and let it be copied. Once copied and confirmed, you can delete the original on the internal drive.

This leaves aside the other strategy of only moving the Masters, and leaving the library, ex masters, on the internal as a Referenced library.

Ernie

Anything else I need to be aware of when moving it?

In addition to Ernie Stamper's advice, check the formatting of your external volume. It needs to be formatted MacOS X Extended. Aperture 3.3.2 will not work with an Aperture library on an external volume formatted differently, and earlier Aperture versions will behave unpredictably, you willbe risking data loss, if your external still has the default FAT32 formatting. And don't put your Aperture Library on a NAS or any other Network volume, see

Aperture: Use locally mounted Mac OS X Extended volumes for your Aperture library

Léonie