Advances in submicron technology make it possible to realize man-made low-dimensional electronic systems with quantum confined energy states, i.e., quantum wires, quantum dots and antidots. With typical confinement energies in the meV regime far-infrared spectroscopy gives a direct access to the quantum confined energy levels in these systems. One is now approaching the limit to prepare quantum dots with well defined small numbers of electrons per dot, N = 1,2,3,.. It becomes thus possible to perform a kind of `atomic' spectroscopy on these systems. We will show in this review that the dynamic excitations in these systems exhibit a very interesting complex interplay of atomic-like single-particle and collective many-body effects.