Cell walls of forages contain a vast reservoir of potential energy that could be available to ruminants to meet their energy requirements. Unfortunately, ruminants are not able to capture all of this potential energy due to the way forages grow and develop. Cell wall formation during the growth and development of the plants is a dynamic process that changes with the stages of development. One can think about the assembly of cell walls much in the same way that a house or building is constructed. There are major scaffolding components—in this case, cellulose fibrils—that set the overall structural dimensions or size and shape of the plant. Other components, hemicellulose, pectin, and proteins, fill in around the fibrils creating and matrix that is flexible and permeable until lignification occurs. Lignin and other phenolics are hydrophobic components that stiffen the wall by driving water out and increasing hydrogen bonding resulting in a rigid less penetrable wall. Incorporation of all components that make up the wall dictates the final form and function of the “fiber” and how it may be used by ruminants.