The current project I'm working on is utilising a third-party ecommerce module with it's own config file. We also have our own config file, so the total config files that are used comes to 3 (including web.config).

For each of our release environments; Dev, QA and Production, each config file will have it's own set of properties and values. Instead of having multiple instances of each file, and maintaining each one, I found a nice little article on merging config template files, with external property files. Read Article

**WARNING**
I came across a very puzzling problem after following the article. I was consistantly getting a "Property evaluation failed." Property 'myProperty' has not been set.

After alot of head scratching, it turns out that all that was needed was to include the xmlns schema attribute in the property files.

<project xmlns="http://nant.sourceforge.net/nightly/latest/nant.xsd">      

</project>