Bryophytes have been evolving in terrestrial and aquatic environments longer than any other group of land plants, surviving and thriving through an incredible range of climatic and environmental variation. Several of the bryophyte growth forms we find today closely resemble those found in ancient fossils whereas many of the other early land plant forms lack modern representatives. What is it about bryophyte growth form and physiology that has allowed them to persist through time and radiate into every terrestrial ecosystem, even dominating some of them? What can we learn from modern bryophytes to address this question and to predict how plants will respond to future environmental change? In this chapter, we briefly examine these questions as a preview to the volume as a whole.