  Magnetic helicity effects are discussed in laboratory and astrophysical
settings. First, dynamo action in Taylor-Green flows is discussed for different
boundary conditions. However, because of the lack of scale separation with
respect to the container, no large scale field is being produced and there is
no resistively slow saturation phase as otherwise expected. Second, the
build-up of a large scale field is demonstrated in a simulation where a
localized magnetic eddy produces field on a larger scale if the eddy possesses
a swirl. Such a set-up might be realizable experimentally through coils.
Finally, new emerging issues regarding the connection between magnetic helicity
and the solar dynamo are discussed. It is demonstrated that dynamos with a
non-local (Babcock-Leighton type) alpha effect can also be catastrophically
quenched, unless there are magnetic helicity fluxes.
