This chapter first describes how small Earth is compared to the rest of the solar system and the universe. Yet, within the confines of the planet Earth, there is a vast array of different living forms that fill many different niches throughout the biosphere. This chapter briefly describes the immense biodiversity on Earth but points out that even though the forms are diverse, the mechanisms by which the business of life is conducted are quite conserved. All living things employ sequences of nucleic acids, either deoxyribonucleic or ribonucleic acids, as the basis for heredity and encoding of proteins that conduct the processes of living.