The processes underlying lignification, which for many years have been the near-exclusive purview of chemists and biochemists, have more recently been approached using both classical forward genetic screens and targeted reverse genetic approaches such as antisense suppression, RNAi, and characterization of insertional mutants. In this review, we provide an overview of the current understanding of lignin biosynthesis and structure, with emphasis on mutant and transgenic plants that have contributed to this knowledge. We also discuss ongoing work aimed at elucidating the relationship between lignin structure and function in vivo, as well as the phenotypic consequences arising from genetic manipulation of the lignin biosynthetic pathway.