This chapter discusses the applications, as well as nanotechnology applications in drilling and completion hardware and cuttings analysis. Drilling and completions represent major capital investments from oil companies, since these are essentially sunk costs that must be committed before any revenue is generated from sales of produced products. When drilling an oil or gas well, drilling fluid must be circulated down through the interior of the drill pipe and back up through the annulus between the drill pipe and formation. Several different types of nanoparticle additives have been investigated to improve the rheology of drilling fluids. Applications focused on improving mudcake quality while reducing the thickness of the mudcake and thus the amount of filtrate invasion generally exploit synergistic effects between nanoparticles and bentonite in the drilling fluid through electrostatic effects. If the density of drilling fluid is too large, the pressure in the wellbore may fracture the surrounding formation.