Thermal stability of 50 ionic liquids (ILs) has been analyzed using a Perkin Elmer thermogravimetric device. Several families with fixed anions and different cations and vice versa were chosen to provide a comprehensive knowledge of thermal properties of ILs against structure. For all the selected ILs, dynamic scans were performed under air atmosphere and a heating rate of 10 K · min−1 to estimate the short-term thermal stability. Isothermal studies were also carried out for some of the above compounds, at temperatures lower than onset temperature (Tonset), in order to evaluate the long-term thermal stability. One of the most used parameters to characterise the long-term thermal stability of an IL is Maximum Operation Temperature (MOT). Because the estimation of this parameter involves the calculation of the activation energy of the degradation process, the kinetics of some of the ILs was analyzed by using different dynamic kinetic methods (Kissinger, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Friedman), and the obtained energy values were compared to those obtained through isothermal methods. There was relatively good concordance in the values of MOT using different criteria.