Anisotropic Scaling in Depinning of a Flux Line

We study the depinning of a flux line by analytical and numerical methods. Transverse fluctuations do not influence the critical behavior of the longitudinal component justifying "planar approximations." In an isotropic medium, longitudinal fluctuations have a roughness exponent ${\zeta }_{\parallel }=1\mathrm{}$, and relax with a dynamic exponent $z_{\parallel }\approx \frac{4}{3}$; transverse fluctuations are suppressed (${\zeta }_{\perp }=\frac{1}{2}<{\zeta }_{\parallel }$), and relax more slowly, with $z_{\perp }=z_{\parallel }+1\mathrm{}$. Anisotropy in the depinning threshold, or orientational dependence of force-force correlations, lead to new universality classes.