Abstract: Objective-C is a very thin layer on top of C. Objective-C is a strict superset of C. That is, it is possible to compile any C program with an Objective-C compiler. Objective-C derives its syntax from both C and Smalltalk. Most of the syntax (including preprocessing, expressions, function declarations, and function calls) is inherited from C, while the syntax for object-oriented features was created to enable Smalltalk-style messaging. Today it is used primarily on Mac OS X, iPhone OS, and GNUstep, which makes this presentation a good intro to the next presentation in the program; "How to build an iPhone app in 45 mins".