Two-dimensional electron systems (2DES) are excellent probes for magnetic fields which vary on a submicron scale. For example, a lithographically defined array of periodically arranged micromagnets, placed on top of a semiconductor heterojunction, gives rise to pronounced oscillations in the resistivity of the 2DES if an externally applied (homogeneous) magnetic field is varied. This ballistic effect, observed at low temperatures, is due to the commensurability between the period of the magnetic stray field (‘z-component’) and the cyclotron radius of the electrons. Information about an individual micro-or nanomagnet can be obtained, e.g., by employing the Hall-effect, an effect usable also at room temperature. We utilize the Hall effect both for micro-Hall-magnetometry by placing microscopic magnets on a sub-micron sized Hall cross containing a 2DES (see electron micrograph below) and microscopy by scanning Hall sensors across magnetic surfaces (scanning Hall-microscopy). Besides an overview on this type of transport experiments I will briefly discuss two other methods, magnetic force and Lorentz microscopy, which we used to get magnetic information about individual micro- and nanomagnets.