Aqua Human Interface Guidelines

This document describes what you need to do to design your application for Aqua, the Mac OS X user interface. Primarily intended for Carbon and Cocoa developers who want their applications to look right and behave correctly in Mac OS X, these guidelines provide examples of how to use Aqua interface elements.

see http://developer.apple.com/documentation/UserExperience/Conceptual/AquaHIGuidelines/