  Do disk galaxies exist at redshifts much greater than unity, and how might
they look different from local disks? How does the morphological mix of
galaxies change with redshift? What can we learn from current observations
about the properties of high redshift galactic disks? I present theoretical
predictions based on semi-analytic hierarchical models, focussing on the role
played by interactions, mergers, and starbursts in determining the observable
properties of disk galaxies at high redshift, and discuss the interpretation of
high redshift observations of possible proto-disks (damped Lyman-$\alpha$
systems and Lyman-break galaxies) in light of these predictions.
