IBM Informix Documentation
Here you can find the documentation for Informix versions 14.10, 12.10, 11.70 and 11.50.
You have online access to the IBM Knowledge Center, can view the documentation as PDF or download it as a packed documentation CD directly here.
Please select the Informix version you are interested in:
Informix 14.10 Documentation
Informix 12.10 Documentation
Informix 11.70 Documentation
Informix 11.50 Documentation
The IBM RedBooks for Informix are a good supplement to the documentation. The Informix RedBooks are usually written by Informix developers and address specific topics. Here is a selection of the interesting IBM RedBooks for Informix. The IBM RedBooks are free for download.