Software plays a major role in safety critical applications from fly-by-wire airplanes, automobile computers, and cruise ship controls to controlling power plants and medical devices. Software can be at various levels of criticality. The FAA uses the DO-178B Guidelines for Safety Critical Applications to determine the criticality level and provide guidance to the software developers through out the software development process. DO-178B is currently being adapted by other industries for use in the development of safety critical software applications. This paper introduces development of safety critical applications including an overview of the DO-178B process. It will also cover the use of DO-178B standard in an object-oriented iterative software development process. The advantages of using an iterative process in the development of safety-critical software will also be highlighted.