This reprint focuses on proteins as critical components of plant cell walls. They contribute not only to the overall architecture of the walls but also to the rearrangement of the cell wall polymers to enable growth, differentiation, and appropriate responses to biotic and abiotic stresses, thus allowing the adaptation of plants to their changing environment. Different experimental approaches are illustrated and the roles of a set of protein families are described. Moreover, new concepts involving the role of cell wall proteins in organ morphogenesis through calcium signaling are discussed.