Conifers from regions with cool-moist summers (all mountains and the boreal conifer belt) are a suitable source of material for building a radiodensitometric tree-ring network in the northern hemisphere north of 40° latitude. Intra-annual densities from rings as small as 30 microns can be analysed using recently improved densitometric techniques. Networks of living conifers provide densitometric data that can be calibrated against instrumental temperatures and rigorous statistical comparisons clearly demonstrate that these data can be used to represent spatial patterns of temperature variability on annual and decadal timescales over, at least, the last 400 years. Continuous multimillennial chronologies of densitometric data are currently under construction in areas such as the Alps, northern Fennoscandia and Siberia (both the Yamal and Taimyr Peninsulas). Large numbers of logs and stumps that could provide material for the construction of many further high-quality multimillennial chronologies are known to exist in river sediments and lakes in the permafrost zone of northern Russia. Subfossil spruce in the boreal zone of northern North America are apparently rare. Relatively little densitometry has been undertaken in the southern hemisphere and what limited results have been produced seem to indicate that densitometric data offer little additional information, at least as regards temperature sensitivity, above that provided by more commonly analysed tree-ring width data.