Gravity provides a directional stimulus that plays an important role in basic life processes in the cell, such as biosynthesis, membrane exchange, and cell growth and development. It is likely that the growth and development of plants are determined by hormones, whose transport is also influenced by gravity. Will these functions develop normally when deprived of the gravitational stimulus? This chapter reviews the fundamental questions raised in the space environment in the areas of gravitational biology, developmental biology, plant biology, and radiobiology (Fig. 2.1). For more details, the readers are referred to the book on Fundamentals of Space Biology by Clément and Slenzka (2006).