In some cases, chapters offer thorough surveys of numerous works involving certain subjects, such as imagined vehicles, journeys beneath the Earth and undersea adventures, discovering intriguing patterns in the ways that various writers developed their ideas. When comprehensive coverage of ubiquitous topics such as robots, aliens and the planet Mars is impossible, chapters focus on major themes referencing selected texts. A conclusion discusses other science fiction subjects that were omitted for various reasons, and a bibliography lists additional resources for the study of science fiction in general and the topics of each chapter.