Answer by Geeky Ninja for What is the difference between String and string in C#?

String: A String object is called immutable (read-only) because its value cannot be modified once it has been created. Methods that appear to modify a String object actually return a new String object that contains the modification. If it is necessary to modify the actual contents of a string-like object

string: The string type represents a sequence of zero or more Unicode characters. string is an alias for String in the .NET Framework. string is the intrinsic C# datatype, and is an alias for the system provided type "System.String". The C# specification states that as a matter of style the keyword (string) is preferred over the full system type name (System.String, or String).Although string is a reference type, the equality operators (== and !=) are defined to compare the values of string objects, not references. This makes testing for string equality more intuitive. For example:

Difference between string & String:

• The string is usually used for declaration while String is used for accessing static string methods
• You can use 'string' do declare fields, properties etc that use the predefined type 'string', since the C# specification tells me this is good style.
• You can use 'String' to use system-defined methods, such as String.Compare etc. They are originally defined on 'System.String', not 'string'. 'string' is just an alias in this case.
• You can also use 'String' or 'System.Int32' when communicating with other system, especially if they are CLR-compliant. i.e. - if I get data from elsewhere, I'd de-serialize it into a System.Int32 rather than an 'int', if the origin by definition was something else than a C# system.