We present a measurement of the scale-dependent, three-dimensional structure
of the magnetic field fluctuations in inertial range solar wind turbulence with
respect to a local, physically motivated coordinate system. The Alfvenic
fluctuations are three-dimensionally anisotropic, with the sense of this
anisotropy varying from large to small scales. At the outer scale, the magnetic
field correlations are longest in the local fluctuation direction, consistent
with Alfven waves. At the proton gyroscale, they are longest along the local
mean field direction and shortest in the direction perpendicular to the local
mean field and the local field fluctuation. The compressive fluctuations are
highly elongated along the local mean field direction, although axially
symmetric perpendicular to it. Their large anisotropy may explain why they are
not heavily damped in the solar wind.