Summary

Basic Properties of Tachocline:

• Interface of rigidly-rotating radiative zone and differentially-rotating convection zone

• May be source of Sun's toroidal field

Observations and Variability

• Helioseismology, Lithium abundance

• 1.3 year semi-periodic cycle

Theoretical Problems

• Thinness of zone

• Lack of diffusion

Potential Solutions

• Magnetic field constraint

• Anisotropic Turbulence