In this review paper, the concept of structural hierarchy is applied to paper in an effort to establish the role of the fibre in the structure of paper . The structure of paper is partitioned according to the size or scale of the features of interest, and the basic nature of a generic paper physics research project is shown to be independent of the scale being considered. The literature dealing with paper structure and properties at each significant scale is briefly introduced, and the similarity of studies at quite different ends of the spectrum is highlighted. The prospects for an integrated model relating a mechanical property such as modulus to structural variables alone are discussed. Throughout the emphasis is on mechanical properties, and the central role of the fibre within the structural hierarchy.