  We first define a complex angle between two oriented spacelike planes in
4-dimensional Minkowski space, and then study the constant angle surfaces in
that space, i.e. the oriented spacelike surfaces whose tangent planes form a
constant complex angle with respect to a fixed spacelike plane. This notion is
the natural Lorentzian analogue of the notion of constant angle surfaces in
4-dimensional Euclidean space. We prove that these surfaces have vanishing
Gauss and normal curvatures, obtain representation formulas for the constant
angle surfaces with regular Gauss maps and construct constant angle surfaces
using PDE's methods. We then describe their invariants of second order and show
that a surface with regular Gauss map and constant angle $\psi\neq 0\ [\pi/2]$
is never complete. We finally study the special cases of surfaces with constant
angle $\pi/2\ [\pi],$ with real or pure imaginary constant angle and describe
the constant angle surfaces in hyperspheres and lightcones.
