For the construction of tunnels or for underground mining applications, for example during gate road development mining or during retread mining at room and pillar mining method, frequently long, straight tunnels, adits or drifts have to be mined. Common haulage methods in underground mines usually are at least partly discontinuous by using patch hauling vehicles. In order to provide a high capacity continuous haulage solution for continuous underground mining applications, Sandvik Mining and Construction G.m.b.H. decided to develop the novel “Extendable Belt System”. This Extendable Belt System represents an extendable belt conveyor system, which is suitable for straight hauling geometries and for rough conditions in underground mines, where additionally space can be very restricted. The goal is to feature the ability of continuous conveying conjunct to the ability to dynamically extend the conveying length. Hereby a belt loop take-up unit, which can be located in line or angled 90 degrees to the conveyor, provides additional belt length while the boot end with the tail pulley is proceeding. In order to control the lateral behavior of the conveyor belt, at problematic sections applicable methods have to be found to provide reliable belt tracking. As a result of intensive studies regarding belt tracking, a descriptive, mainly geometrical explanation of the lateral behavior of belt tracking at cylindrical, conical and crowned pulleys in general is given. Regarding belt tracking, also a principal description of the geometrically proper arrangement of two adjacent pulleys which guide a common belt is given. Based on this description, the geometrical proper conditions of a set-up, where a belt is deflected to an arbitrary direction by using three pulleys, are described. Based on the novel knowledge regarding belt tracking as described in this thesis, the new, modular as well as flexible concepts of a “T- Type Lateral Belt Deflection Device” and of an “L- Type Lateral Belt Deflection Device” have been developed.