A new grid of theoretical isochrones based on the Yale stellar evolution code using the OPAL and Kurucz opacities has been constructed .
The grid of isochrones spans a wide range of metallicities , helium abundances and masses .
The construction of the isochrones is described and the isochrones are compared to galactic globular cluster observations .
A solar calibrated mixing length ( \alpha = 1.7 ) yields a good fit to globular cluster colour-magnitude diagrams .
Ages for 40 globular clusters are determined using the \Delta { V } ( { TO } - { HB } ) method and the formation of the halo is discussed .