NSString is decades old, from NeXTSTEP (you can see that in the name: "NS"). While its possible they could change it, the in-memory representation doesn't matter much in this case. When you transfer data out, such as with writeToFile:encoding: or convert it into a char * (often with UTF8String, or one of the C string methods), you are almost always specifying an encoding anyway. And, for most Cocoa apps, that encoding is UTF8.