This paper expounds the basics of isotope fixation in tree rings and relevant field and laboratory procedures. Examples from high mountain regions show both the potential and limits of employing these methods in dendroclimatological studies. Carbon isotopes yield seasonally resolved information on temperature, precipitation and relative humidity, whilst oxygen isotopes provide information on the isotope values of the source water, and thus, on precipitation. Inter-annual and decadal variations, in particular, reflect a strong common climatic signal that extends across a wide range of site ecologies. However, low frequency trends are masked by a non-climatic, human induced long-term trend, especially where carbon isotopes are concerned. At present, detrending methods are of a provisional nature and set a limit to stable isotopes for paleoclimatic questions. Highly resolved plant physiological and biochemical investigations should provide more insight into these unsolved problems.