What's the difference between the WebConfigurationManager and the ConfigurationManager?

WebConfigurationManger knows how to deal with configuration inheritance within a web application. As you know, there could be several web.config files in one applicaion - one in the root of the site and any number in subdirectories. You can pass path to the GetSection() method to get possible overridden config.

If we'd looke at WebConfigurationManager with Reflector then things are clear:

public static object GetSection(string sectionName)
{
    ...
    return ConfigurationManager.GetSection(sectionName);
}

public static object GetSection(string sectionName, string path)
{
    ...
    return HttpConfigurationSystem.GetSection(sectionName, path);
}

WebConfigurationManager is made specifically for ASP.NET applications.

WebConfigurationManager provides additional methods to load configuration files applicable to Web applications.

ConfigurationManager provides also methods to load configuration files applicable to ".exe" applications.

I’d suggest taking a look at WebConfigurationManager and see if it provides you with anything you simply cannot do with ConfigurationManager and use it instead, otherwise using ConfigurationManager will make it far easier to have your code be used seamlessly between web and desktop aps.

Although WebConfigurationManager is located in the System.Web assembly the ConnectionStringSettingsCollection that it returns is located in System.Configuration.

If you are getting the error

Cannot apply indexing with [] to an expression of type 'System.Configuration.ConnectionStringSettingsCollection'

while trying to access the array index...

WebConfigurationManager.ConnectionStrings["Name"].ConnectionString

make sure you have a reference to assembly System.Configuration