The transition from forest to tundra in Arctic and alpine regions, frequently referred to as treeline, has preoccupied biogeographers and ecologists for more than a century. It is widely hypothesized that treelines will advance in response to current and anticipated future temperature increases worldwide. Monitoring of these ecotones is important in light of the potential for change. Equally important is an understanding of past changes so that future changes and their impacts can be forecast. This paper provides an overview of methods that have been used to detect and measure change at forest–tundra ecotones worldwide, with examples drawn from studies of treelines in alpine areas of the subarctic. These methods include resurveys of field plots and transects, repeat photography, dendrochronology, use of historical records, remote sensing, and paleoecological techniques such as palynology and subfossil analysis. The benefits and limitations of each approach are identified and evaluated. It is shown that there is no single best method, largely because each is only capable of resolving change within a specific range of temporal and spatial extents. Multiscale approaches that integrate several methods and techniques provide a more comprehensive picture of change and can be used to identify the variables that influence treeline dynamics and better understand functional mechanisms of response.