Recent advances on the understanding of properties of nanocontacts involving metal atoms and molecules are discussed. Different ways of generating these nanocontacts are discussed, as well as different theoretical approaches devoted to their study. Special emphasis is made on the measurement and the calculation of electrochemical properties. The reason for this is that the electrochemical environment appears as particularly suited for the design of devices like nanoswitches and nanosensors. The most generally accepted models and hypothesis are given, but emphasis is also made on some items subject of hot discussion in the field.