Nanoparticle superlattices are hybrid materials composed of closely packed inorganic particles separated by short organic spacers and they have unique electronic, optical, magnetic and remarkable mechanical properties. Two-dimensional arrays of close-packed nanoparticles can be stretched across micrometre-size holes and the resulting free standing monolayer membranes can extend over hundreds of particle diameters without crosslinking of the ligands or further embedding in polymer. The physical properties of metal nanoparticle superlattices are predominated by particle size, interparticle spacing, and superlattice symmetry (overlap of wave function). For example dodecanethiol-ligated 6-nm-diameter gold nanocrystal monolayers have a Young’s modulus of the order of several GPa and have high flexibility, enabling the membranes to bend easily while draping over edges. The arrays remain intact and able to withstand tensile stresses at elevated temperatures making them excellent candidates for wide range of sensor applications. With nanoparticle superlattices it is possible to generate future nanodevices with low-cost and low-energy consumption.