  Our understanding of processes occurring in the heliosphere historically
began with reduced dimensionality - one-dimensional (1D) and two-dimensional
(2D) sketches and models, which aimed to illustrate views on large-scale
structures in the solar wind. However, any reduced dimensionality vision of the
heliosphere limits the possible interpretations of in-situ observations.
Accounting for non-planar structures, e.g. current sheets, magnetic islands,
flux ropes as well as plasma bubbles, is decisive to shed the light on a
variety of phenomena, such as particle acceleration and energy dissipation. In
part I of this review, we have described in detail the ubiquitous and
multi-scale observations of these magnetic structures in the solar wind and
their significance for the acceleration of charged particles. Here, in part II,
we elucidate existing theoretical paradigms of the structure of the solar wind
and the interplanetary magnetic field, with particular attention to the fine
structure and stability of current sheets. Differences in 2D and 3D views of
processes associated with current sheets, magnetic islands, and flux ropes are
discussed. We finally review the results of numerical simulations and in-situ
observations, pointing out the complex nature of magnetic reconnection and
particle acceleration in a strongly turbulent environment.
