The CanoScan 8400F is not compatible with Mac OS X 10.7 Lion or Mac OS X 10.8 Mountain Lion. It is compatible with all versions of OS X before this. Here are the steps to download:
1. Visit Canon's web site at:
2. Click on SUPPORT & DRIVERS. On the Support & Drivers page, select your model in the following manner:
a. From the first menu, select SCANNERS.
b. From the second menu, select CANOSCAN SERIES.
c. From the third menu, click DRIVERS & SOFTWARE beside CANOSCAN 8400F.
3. Select Mac OS using the drop down menu SELECT OPERATING SYSTEM VERSION, then select your version of OS X using the SELECT OS VERSION drop down box.
4. Click DRIVERS to display the drivers available.
5. Click on 8400F Scanner Driver.
6. Instructions for completing the download and installation will appear on the page that follows. You will also see a disclaimer at the bottom. Review the disclaimer, and click I AGREE - BEGIN DOWNLOAD.
7. Once the download is complete, double click on the downloaded file to start the installation. Follow the onscreen instructions to install.
If you have a version of OS X that is not compatible,you would be eligible for service options. To hear about these, please click the following link: