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The new availability of (1) multicolor isochrones and (2) a correct understanding of interstellar broadband extinction in all colors make possible an entirely new technique of uniquely determining the interstellar reddening, the distance modulus, and the age and metallicity parameters of reasonably coeval stellar populations. The method requires the use of (1) spectroscopically calibrated colors for the transformation of theoretical isochrones to observational using Kurucz fluxes, (2) robust statistics to derive likelihood estimates in the simultaneous fit, (3) variable reddening of the isochrone at each value of each color index to obtain the correct placement of the isochrone in each color--magnitude diagram at each point. We show successful examples of the use of the technique on the red giant branches of old populations and on the main sequences of young populations, in two different broadband systems, Johnson--Cousins and Washington.
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