This study aims to investigate the adsorption of nanoparticles at the solid-water interface. Surface treatments with nanoparticles have been increasingly explored for a broad range of potential applications. However, the adsorption behaviour of inorganic nanoparticles has not been well studied to-date. Nanoparticle adsorption can be affected by several factors, such as the type of solid substrate, nanoparticle shape, nanoparticle concentration and salt concentration in the nanoparticle suspension, Two types of nanoparticles are used in this thesis: spherical Ludox silica (20 nm) and disk-like laponite clay (25 nm across, 1 nm thick). The adsorption of Laponite nanoparticles at the solid-water interface on various substrates and over a range of Laponite concentrations has been investigated using a quartz crystal microbalance (QCM) and an optical reflectometer (OR). Adsorption of laponite was only observed on a positively charged poly(diallyldimethylammonium chloride) (PDADMAC) surface, whereas no adsorption was seen on hydrophilic/hydrophobic, negative or neutrally charged surfaces. This shows that when fully wetted, Laponite adsorption depends primarily on the surface charge. The adsorption of both Laponite and Ludox silica onto PDADMAC coated surfaces over the first few seconds were studied by OR. The initial adsorption rate of Laponite was faster than Ludox, possibly due to reorientation of the laponite nanoparticles as they approach the substrate. Over longer times, the QCM data for Ludox III nanopartic1es demonstrated more complex adsorption behaviour than Laponite, demonstrating intermixing processes taking place within the PDADMAC-Ludox layer. The effect of a monovalent salt (NaCI) on the adsorption behaviour of both PDADMAC and Ludox nanopartic1es was also investigated using QCM. These data suggest that the adsorbed amount of Ludox increase with NaCI concentration. This can be explained by the roughening of the PDADMAC surface at high salt concentrations leading to more Ludox nanopartic1es adsorbing per unit area. Preliminary evidence for less intermixing between the PDADMAC and the Ludox when the PDADMAC layer was adsorbed and then pre-dried was also found.