Background is provided on what dendrochronology entails. The binocular microscope is used for measuring the tree-ring width; at the Laboratory of Tree-Ring Research at the University of Arizona, the state-of-the-art equipment, interfaced with microcomputers that are hooked up to mainframes, provides efficient statistical treatment. Standardization, calibration, and verification are part of the reconstruction strategies. An evaluation of the worldwide tree-ring database indicates the spatial availability of tree-ring data as of 1980 for climatic reconstruction. A survey of dendroclimatology applications illustrates how the data have been used. The appendix discusses palaeoclimatic studies using isotopes in trees. Tree-ring isotope chemistry is a new area of research that has significantly contributed to palaeoclimatic studies. The tools for these investigations are the isotope ratios derived from the carbon isotopes, oxygen isotopes, and hydrogen isotopes incorporated in the cellulose. Direct correlations have been made between stable isotope ratios and climatic data; carbon-14 research of tree-ring cellulose has provided new information on solar variability. The methodology is discussed.