1.  Introduction
    1.1  Current empirical limit

2.  Predictions in the homogeneous limit

3.  Inhomogeneous limit:  No mixing

    3.1  The fraction of Population III stars
    3.2  The low-metallicity threshold

4.  Interstellar dispersal

    4.1  Diffusion
    4.2  Turbulent mixing
    4.3  The dispersal of metals

5.  Inhomogeneous limit:  Dispersal by mixing

    5.1  Mixed-dispersal, high-evolution SIM
    5.2  Mixed-dispersal, low-evolution model

6.  Discussion

    6.1  The low-metallicity threshold
    6.2  The fraction of Population III stars
    6.3  Predicted and observed MDFs
    6.4  Halo evolution

7.  Conclusion