INTRODUCTION Many basic chemical principles are important to the understanding and study of plant cell biology. Chemistry is the study of matter. Anything you can touch, see or smell is a form of matter. Matter can be thought of as anything that has mass and volume. Matter is typically classified by the state of the matter: solid, liquid, or gas. All matter is composed of chemicals and the study of chemicals is the field of chemistry. This chapter provides an overview of some of the key topics in chemistry as they relate to plant cell biology. More detailed discussions of these topics can be found in chemistry texts. Topics to be discussed include basic concepts of elements and molecules with a focus on water and its properties. The environment in which plants grow and the large amount of water present in plants dictates a need for a clear understanding of water and some of its unique properties.