Plant anatomy has a long history in France and after being considered for a few decades as too “old fashioned”, it is now regaining some popularity. In this talk, we will present examples of how we use plant anatomy in our department to understand the affinities and biology of both living and extinct plants. This research uses classical preparation methods of plant organs, including fossils in which the tissues have been preserved, often combined with improved instruments and methods for observation and analysis. Anatomy is a fundamental part of our paleobotanical studies, since it is the only information available to assess the affinities of some fossil plants and to fully understand the evolution of major groups. In the case of extant plants, fine anatomical details can also play a key role in discriminating between related taxa, with important implications for plant conservation. Plant anatomy is also crucial to understand how plants function and interact with their environment. We will discuss the link between draught resistance and xylem anatomical traits in stems and leaves, the question of the trade-off between hydraulic conductivity and mechanical support, and how we can investigate the hydraulic properties of some of the oldest fossil woods. We will also present recent studies on the biomechanical properties of (1) liana self-supporting searcher shoots and (2) 250 Ma fossil roots, and we will discuss their interest for developing new technologies inspired from plant organs. Finally, we will illustrate recent studies of wood anatomy and tree growth in various present and past environments.