Electrical impedance spectroscopy (EIS) is a method for measuring cold hardiness of plants. It has been widely used in the fields of agriculture, forestry and horticulture. In this paper the following aspects were introduced and discussed: (1) physical and physiological factors of impedance measurements in plants, (2) suitable models for measuring EIS, and (3) method for assessing cold hardiness by means of EIS. In traditional EIS analysis, after completion of the artificially controlled freezing tests, the extracellular resistance (r(e)) is the best parameter for determining cold hardiness of plants. It has been reported recently that cold hardiness might be determined just after sampling using EIS analysis without a controlled freezing test. The relaxation time (tau(1)) is the most suitable parameter: in the rapid hardening phase, differences in the hardening patterns of various provenances of Scots pine (Pinus sylvestris L.) could be distinguished by the relaxation time with an accuracy of +/-2 degrees C without a controlled freezing test.