Superconductivity in high-T_c oxides originates from the presence of (CuO₂)-planes which lead to highly anisotropic normal and superconducting transport properties. The short coherence length ξ_c ≈ 1 to 3Å causes a spatial variation of the order parameter along the c-direction with dramatic consequences on the vortex dynamics. As model systems to study the influence of structural changes we prepared epitaxial YBa ₂( Cu _1−x TM _x)₃ O ₇ films ( TM = Zn and Ni), Bi ₂ Sr ₂ CaCu ₂ O ₈ films and coherent YBa ₂ Cu ₃ O ₇/ PrBa ₂ Cu ₃ O ₇ superlattices. Measurements of the critical current density [Formula: see text] clearly reveal the intrinsic pinning mechanism in YBa ₂ Cu ₃ O ₇ for B ⊥ c at low temperatures which disappears approaching T_c. Small transition metal dopings act as pinning centers reducing dissipation due to thermally activated flux movement. The decoupling of the (CuO₂)-layers in the superlattices causes a transition from anisotropic 3d to 2d behavior. Therefore the superconducting properties in external magnetic fields, which resemble closely those of Bi ₂ Sr ₂ CaCu ₂ O ₈ films, are dominated by the field component parallel to the c-axis. For B ⊥ c the resistive transitions ρ (B, T) and the critical current density j_c (B, T) are nearly field independent.