There has been recent progress in the study of the angular momentum evolution of low mass stars ( Krishnamurthi et al 1997a ) .
Theoretical models can now be constructed which reproduce the angular momentum evolution of low mass open cluster stars and the distribution of initial conditions can be inferred from young clusters .
In this poster we report on the application of these models to the problem of rotational mixing in halo stars .

The distribution of initial conditions inferred from young clusters produces a well-defined halo lithium “ plateau ” with modest scatter and a small population of outliers .
Different choices for the solar calibration produce a range of absolute depletion factors .
We show that both the dispersion and the ratio of ^ { 6 } Li depletion to ^ { 7 } Li depletion increase as the absolute ^ { 7 } Li depletion increases .
The measured ^ { 6 } Li in HD 84937 and the dispersion in the plateau set independent upper bounds on the ^ { 7 } Li depletion .
Consistency with open clusters and the Sun , along with claims of an intrinsic dispersion in the plateau , set a lower bound .
We derive a range of 0.2-0.4 dex ^ { 7 } Li depletion in halo field stars .
Implications for cosmology are discussed .