Unless I misunderstood it, this LINK from Apple's documentation clearly states that the class initializer, "+ (void)initialize)", only executes once per class. Here is the excerpt: Special Considerations initialize it is invoked only once per class. If you want to perform independent initialization for the class and for categories of the class, you should implement load methods. However, I'm getting a weird behavior on my project and the initializer is being executed twice. So I have to check if _classContext is null. I only got one class that has this method. What are the possible reasons why this is happening? I'm using XCode 4.5.2 and OS X 10.8.2. I got multiple iOS simulators, iPhone 5.1 and 6.0. + (void) initialize { num++; NSLog([NSString stringWithFormat:@"Times: %i", num]); if(_classContext == nil) _classContext = [[myClass alloc] init]; }