As a consequence of moving from aquatic to terrestrial ecosystems, plants evolved superb mechanisms for protecting their structural polymers from attack by the microbial and animal world.  We know that that this protection can be explained in a general sense as one of structure and chemistry at multiple length scales.  Protection from deconstruction is conferred first by rind or bark, then by thickened cells surrounded by lignins, then the chemical complexity of cell walls, and finally by the insolubility of cellulose itself.  We also have some understanding of the various thermal chemical, mechanical, and enzymatic treatments of plant cell walls, but primarily in the context of applying empirical results to biomass processing schemes.  This state of the art will be reviewed.  However, our need as a community to truly understand such phenomena at the molecular scale will also be discussed.  A point can be made that it is only through the acquisition of such knowledge that true manipulation of the biosphere can ultimately be accomplished.