A theory of step meandering on a vicinal surface is developed. At equi
librium, the meander w similar to [ln(L)](1/2), where L is the lateral
extent. During step flow growth, the diffusive repulsion prevails ove
r elasticity. It leads to new scaling laws for the meander w as a func
tion of the interstep distance I, etc. For a weak Schwoebel effect, we
find w similar to l(1/4) (at equilibrium w similar to I). The diffusi
ve repulsion behaves as l lnl. Dynamics tend to ''cure'' meandering. A
t higher growth speed, deterministic roughening intervenes. In this re
gime we derive general nonlinear equations for interacting ''lines.''
Disordered structures seem to prevail.