This protocol defines the interface for so-called first-class objects. Objects that conform to the NSObject protocol are able to provide a great deal of information about themselves to other objects, such as their classnames, superclass names, and the protocols that they conform to. Additionally, this protocol declares methods that clients use to determine whether an object can respond to an arbitrary message. Finally, the NSObject protocol declares methods that allow objects to participate in Cocoa's memory management system. In the Foundation framework, the two root classes NSObject and NSProxy conform to this protocol.

@protocol NSObject
// Instance Methods
- (BOOL)isEqual:(id)object;
- (unsigned)hash;
- (Class)superclass;
- (Class)class;
- (id)self;
- (NSZone *)zone;
- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;
- (BOOL)isProxy;
- (BOOL)isKindOfClass:(Class)aClass;
- (BOOL)isMemberOfClass:(Class)aClass;
- (BOOL)conformsToProtocol:(Protocol *)aProtocol;
- (BOOL)respondsToSelector:(SEL)aSelector;
- (id)retain;
- (oneway void)release;
- (id)autorelease;
- (unsigned)retainCount;
- (NSString *)description;
@end