Plants are a huge and diverse group of organisms, ranging from microscopic marine phytoplankton to enormous terrestrial trees epitomized by the giant sequoia: 300 feet tall, living 3000 years, and weighing as much as 3000 tons. For this plant issue of "CBE-Life Sciences Education," the author focuses on a botanical topic that most people, even biologists, do not think about--plant behavior. The author begins by defining what a plant is and then delves into the behaviors of plants.