This book is intended as an overview at an undergraduate or early university level and describes the effects of spaceflight at cellular and organism levels. Past, current, and future research on the effects of gravity - or its absence - and ionizing radiation on the evolution, development, and function of living organisms is presented in layman's terms by researchers who have been active in this field. The purpose is to enlighten science and non-science readers to the benefits of space biology research for conducting basic and applied research to support human exploration of space and to take advantage of the space environment as a laboratory for scientific, technological, and commercial research. The first chapters present an overview of the major focuses of space research in biology, as well as the history and the list of animals and plants that have flown in space to date.