One of the most widely studied types of magnetic nanostructure is that used in devices based on the giant magnetoresistance (GMR) or tunnel magnctoresistance (TMR) phenomena. In order to understand the bchavi.our of these materials it is important to be able to follow their magnetization reversal mechanism, and one of the techniques enabling micromagnetic studies at the sub-micron scale is transmission electron microscopy. Two techniques can be used: Lorentz transmission electron microscopy and off-axis electron holography, both of which allow the magnetic domain structure of a ferromagnetic material to be investigated dynamically in realtime with a resolution of a few nanometres. These techniques have been used in combination with in situ magnetizing experiments, to carry out qualitative and quantitative studies of magnetization reversal in a range of materials including spin-tunnel junctions, patterned thin film elements and magnetic antidot arrays. Quantitative analysis of the Lorentz TEM data has been carried out using the transport of intensity equation (TIE) approach.