Where to declare/define the database connection part in C#

Typically, database connection information is configurable and is thus not "hardcoded" inside your app. If you want to hardcode the connection string, define a constant somewhere in your data access layer. If you wish to cache configuration data instead, you probably should implement it using the singleton pattern. Have a look at the Microsoft Configuration AppBlock to see how it all works (or just use the block directly). http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/cmab.asp regards, Dominique Leblond