  We employ a high-resolution LCDM N-body simulation to present merger rate
predictions for dark matter halos and investigate how common merger-related
observables for galaxies--such as close pair counts, starburst counts, and the
morphologically disturbed fraction--likely scale with luminosity, stellar mass,
merger mass ratio, and redshift from z=0 to z=4. We provide a simple
'universal' fitting formula that describes our derived merger rates for dark
matter halos a function of dark halo mass, merger mass ratio, and redshift, and
go on to predict galaxy merger rates using number density-matching to associate
halos with galaxies. For example, we find that the instantaneous merger rate of
m/M>0.3 mass ratio events into typical L > f L* galaxies follows the simple
relation dN/dt=0.03(1+f)(1+z)^2.1 Gyr^-1. Despite the rapid increase in merger
rate with redshift, only a small fraction of >0.4 L* high-redshift galaxies
(~3% at z=2) should have experienced a major merger (m/M >0.3) in the very
recent past (t< 100 Myr). This suggests that short-lived, merger-induced bursts
of star formation should not contribute significantly to the global star
formation rate at early times, in agreement with observational indications. We
emphasize that great care must be made in comparisons to observations because
the predicted observables depend very sensitively on galaxy luminosity,
redshift, overall mass ratio, and uncertain relaxation timescales for merger
remnants. We show that the majority of bright galaxies at z=3 should have
undergone a major merger (>0.3) in the last 700 Myr and conclude that mergers
almost certainly play an important role in delivering baryons and influencing
the kinematic properties of Lyman Break Galaxies (LBGs). (abridged)
