Decadal-scale oscillatory modes of atmosphere-ocean variability have recently been identified in instrumental studies of the Pacific sector. The regime shift around 1976 is one noteworthy example of a Pacific decadal climatic fluctuation, which has been shown to have significantly impacted climate and the environment along the western Americas. The length of meteorological data for the Pacific and western Americas critically limits such analyses of decadal-scale climate variability. Here we discuss recent studies of decadal-scale oscillations using temperature and precipitation-sensitive tree-ring series from the circum-Pacific spanning the past several centuries. Evaluation of these tree-ring records, from the western coasts of the two Americas, as well as Hokkaido and Kamchatka, reveals a shift towards less pronounced interdecadal variability in the instrumental period, after about the middle 1800s. We have also developed reconstructions of the annual Pacific Decadal Oscillation (PDO) Index based on western North American tree-ring records, which extend as far back as AD 1700. Our analyses suggest that both coastal Alaska and vicinity, as well as the subtropical Americas need to be represented in proxy data sets used to reconstruct the PDO.