The protein paxillinplays a crucial role in the regulation of cell attachment, spreading and motility by providing docking sites for structural and signalling molecules in focal adhesions. Its N-terminal region (33 kD) mediates a variety of protein interactions, often via five short leucine-rich sequences known as 'LD motifs'. The aim of this thesis was to investigate the structure and interactions of this region of paxillin. The entire N-terminal region and various fragments were produced by recombinant methods. Primary sequence analysis, nuclear magnetic resonance (NMR) and small angle X-ray scattering (SAXS) reveal that this region is intrinsically disordered. Long fragments are shown to associate with the focal adhesion targeting (FAT) domain of focal adhesion kinase (FAK). Gel filtration and SAXS were used to study the stoichiometry and shape of the paxillin-FAT complexes formed. Testable structural models involving 1 : 2 stoichiometry are proposed. Another key protein that associates with paxillin LD motifs is actopaxin. The crystal structures of the C-terminal CH-domain of actopaxin (1.05 A.resolution) and its complex with the LD1 motif of paxillin (2.1 A resolution) were solved. It was found that the LD binding site is located at the edge of the canonical CH domain and includes part of the adjacent inter-CH-domain linker. The topology of the binding site is fundamentally different from the LD binding FAT domain, indicating that LD motif recognition does not depend on a conserved fold. The actopaxin-LD-motif interaction was also characterised in solution. This study reveals that all five paxillinderived LD motifs bind to actopaxin, albeit with varying affinities. Paramagnetic relaxation enhancement experiments provide evidence that the same binding site of actopaxin can accommodate LD motifs in either of two anti-parallel orientations. It is suggested that this high degree of binding degeneracy may facilitate the assembly of dynamic signalling complexes in vivo. NMR was also used to explore the structural basis of a number of diverse interactions relevant to the paxillin signalling hub, such as the engagement of actopaxin with actin and the postulated interaction between the FAT domain of FAK and the FERM domain of talin. Further studies concerned the association of the cytoplasmic tails of integrin receptors with the N-terminal region of paxillin, the rod domain of talin as well as type-I PKA. A common theme emerging from these experiments is the notion that the functional properties of integrin-tails may be influenced by their dimerisation and/or clustering at the cell membrane.