Section of Astrogeophysics, Physics Department, University
of Ioannina, Ioannina GR-45110, Greece
Magnetic helicity is a quantity that describes the chiral properties of magnetic structures. It has the unique feature that it is probably the only physical quantity which is approximately conserved even in resistive MHD. In this talk, I will discuss ways that allow us to compute the helicity content of active regions. The importance of helicity in the initiation of solar eruptions will be also discussed.