Format, String.Format and StringBuilder.AppendFormat

Format is Delphi's C-like format function. For example, Format('%s = %d',[MyString, MyInteger]).

String.Format and StringBuilder.AppendFormat are using FCL formatting. For example, String.Format('{0} = {1}', [MyString, MyInteger]).

Refer to http://msdn2.microsoft.com/en-us/library/hdekwk0b.aspx for further FCL Format information.