Long dipole magnets guide the particle beams in synchrotron-type high energy accelerators. In principal it is possible to design and build a set of race-track-like dipolar windings such that the current passing through it will provide a highly uniform magnetic field across the beam line. But in practice parasitic magnetization and currents associated with the superconducting Rutherford cable required for the construction of high-field dipoles produce multipolar distortions (harmonics) of the otherwise pure-dipolar field. Small effective filament diameter (small actual diameter and reduced bridging) can reduce the so-called "persistent-current magnetization" of the multifilamentary strand; it is also possible to ferromagnetically compensate for (or cancel out) the effect of strand magnetization. Generated during changes of dipolar field (field ramping), interstrand coupling currents can also be responsible for the establishment of field harmonics. Such coupling currents are moderated by the resistance of interstrand contact the effective value of which can be controlled by: adjusting the level of native oxidation of the strand, coating the strand, or by inserting a ribbon-like core into the cable to fully or partially separate the strands. These issues are reviewed for cables wound with both low-Tc and high-Tc strands.