Molecular electronics aims at using tailor-built molecules as activedevice elements to achieve the desired electronic functional-ity. Molecular-based electronic switches appear to be the mostpromising candidates for compact memory arrays with low powerconsumption. In the past decade, detailed investigations have beenperformed on a great variety of molecular switches, includingmechanically interlocked switches, conformational switches, andredox-active molecules. In this chapter, we will review basicswitching mechanisms in molecular switches: thermal fluctuations,current-induced excitations, and quantum tunneling. We willdemonstrate how the quantitative information allowing to judgebetween those different switching mechanisms can be extractedfrom the data measured on single-molecule devices. We will alsodiscuss how the intrinsic switching properties may be affectedwhen the molecule is bridged to electrodes, and how to distinguishwhether the switching happens in molecular kernel or at themolecule-to-electrode interface.