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Isochronal fitting (aka isochrone fitting) is determining a star's age based on observable parameters along with stellar evolution models. This can be carried out for a single star or for a stellar cluster, to discover the entire cluster's age. The parameters are matched with a table of model-data that associates combinations of stellar parameter-values with stellar ages and evolutions. The table-data may be from previously-computed evolutions, verified through observation as much as practical. Suitable tables have been made publicly available, such as Dartmouth Stellar Evolution Database (DSED) and BaSTI. The fitting is typically carried out with a few chosen parameters (depending upon what is available for the star(s) of interest) retrieved from observation data, which are compared to the analogous parameters in the table to find a compatible stellar evolution and age. Among the parameters used that have been used: effective temperature, color index, luminosity, metallicity, mass, radius, and density (because stellar density can be derived from extra-solar planet transit light curves).