is a protocol. http://developer.apple.com/documentation/Cocoa/Reference/Foundation/Protocols/NSCoding_Protocol/ Apple's docs on archiving and serialization are here: http://developer.apple.com/documentation/Cocoa/Conceptual/Archiving/ ---- If a class conforms to then it can can be archived. (see UsingArchiversAndUnarchivers) If a class conforms to it implements these required methods (i.e. responds to these messages:) -(id)initWithCoder:(NSCoder*)coder; -(void)encodeWithCoder:(NSCoder*)coder; What these two methods are expected to do: * initWithCoder: initialises an instance of the Class from an NSCoder object. * encodeWithCoder: writes an existing instance of the Class out to an NSCoder object. Most of the foundation classes conform to . For more information on how your class can conform to see the page on NSCoder. ---- I put together a tutorial on NSKeyedArchiver/NSKeyedUnarchiver and NSCoding: http://cocoadevcentral.com/articles/000084.php -- ScottStevenson