When we think of the desert, perhaps we mostly think of large expanses of sand dunes. But only a tiny part of the Earth's deserts are like that. We learn the difference between the two main types of deserts - dry deserts and polar deserts. We also learn where on Earth deserts form. We go through terms like tropic, zenith and rain shadow. All life in the desert has had to adapt to extreme conditions. We find out what traits plants and animals have developed to survive in these places. Finally, we look at some of the changes and challenges that affect the desert.