Ecometrics is a trait-based approach to study ecosystem variability through time.An ecometric value is derived from describing the distribution of functional traits at the community level, which may arise by environmental filtering, extinction, or convergence.An ecometric relationship describes the correspondence between spatially explicit ecometric values and corresponding environmental variation. Transfer functions and maximum likelihood approaches have been developed with modern trait-environment relationships to reconstruct paleotemperature, paleoprecipitation, and paleovegetation cover given the distribution of functional traits within a community. Because the focus for this approach is on the traits and not on species, it is transferable through space and time and can be used to compare no-analog communities. In this paper we review the concepts and history of ecometric analysis and then describe practical methods for implementing an ecometric study.