Connection String for database which exists in asp.net Project:  If you have your database (.mdf) in App_Data Folder then it will work fine. <connectionStrings>   <add name="ConnectionName"     connectionString="Data Source=.\SQLEXPRESS; AttachDbFilename=|DataDirectory|DatabaseName.mdf; Integrated Security=True; User Instance=True" providerName="System.Data.SqlClient"/> </connectionStrings> Please visit to our YouTube Channel for .net and othe tech tutorial Thanks