  A review of some of the issues that have arisen over the years concerning the
energy distribution among scales for magnetohydrodynamics (MHD) turbulence is
given here. A variety of tools are employed to that effect, and a central role
is played by taking into consideration the ideal (non-dissipative) invariants,
namely the total energy, the magnetic helicity and the cross-correlations
between the velocity and the magnetic field (concentrating on the
three-dimensional case). These concepts, based mostly on theory, models and
direct numerical simulations, are briefly put in the context of observations,
in particular the solar wind, and some of the remaining open questions are
delineated as well. New results on ideal MHD dynamics in three dimensions on
equivalent grids of up to $6144^3$ points using the Taylor-Green flow
generalized to MHD are also mentioned.
