I bought Aperture and have it installed on my Macbook. I now also have a Macbook AIR, which I use regularly. Can I also install Aperture on my MacBook AIR, too, without paying for it again?

Yes. Make sure to use the same Apple ID used for the original download.

Instructions > Downloading past purchases from the App Store, iBookstore, and iTunes Store

Did you download Aperture from the AppStore, or do you have a boxed retail version installed? If you did not buy from the App Store, what is your Aperture version?

hi Leonie, I've downloaded it from AppStore, unfortunately.

• If it is the Mac App Store, then Carolyn Samit's solution is perfect. Sign into the App Store on your MacBook Air with the original AppleID you used and install Aperture from the Purchased page.
• But If you bought a serial number and downloaded from the Apple Store, then you cannot download an installer from Apple's sites. In that case your best bet would be to update your current version to Aperture 3.5.1 if you are still using an older version. Updating to 3.5.1 will change your license to a Mac AppStore license, and you can download from the AppStore on your other Mac.

Which Aperture version do you have installed? Are you already using Aperture 3.5.1 on MacOS X 10.9.3?