Electrical conductivity of bulk metals is based on their electronic band structures, and the mobility of electrons is related to their mean free path between two collisions with the lattice. The collective motion of electrons in a bulk metal obeys Ohm’s law, V = RI, where V is the applied voltage, R is the resistance of the material and I is the current. As the electronic band structure changes into discrete energy levels, Ohm’s law is no longervalid. If one electron is transferred to a small particle, the Coulomb energy of the latterincreases by EC = e.sqrd./2C, where C is the capacitance of the particle. If the temperature islow such that kT is less than e.sqrd./2C, single electron tunneling processes are observed.Hence, the I-V characteristic of a quantum dot is not linear, but staircase-like. No currentflows up to VC = ±e/2C. If this value is reached, an electron can be transferred. Following this, an electron tunnelling process occurs if the Coulomb energy of the particle is compensated by an external voltage of V = ±ne/2C. This behaviour is called Coulomb blockade. The charging energy increases with decreasing the size of the quantum dot.Experimental approaches to measure the Coulomb blockade. Two metallic leads with spacing of a few nm are fabricated. An organic monolayer is then used to bind nanocrystals to the leads. When a nanocrystal bridges the gap between the leads, it can be electrically investigated.In voltammetric experiments in solution, metal nanoparticles behave as redox active molecules, showing redox cascades that are well known in inorganic and organometallic electrochemistry.