To achieve the potential for extremely low loss in optical fibers, it is necessary to use alternative materials to those based on silica such as IR transmitting materials. Essentials for the choice of materials are wide transmission range and ultimate loss, together with the need for satisfactory mechanical properties. There are several types of materials which have been investigated for mid-IR fibers: crystalline and vitreous. Crystalline materials are of great interest because of their potenitally wide transmission range and low intrinsic loss. However, their poor mechanical strength and chemical instability bear serious problems for long fiber fabrication. Recently developed heavy metal fluroride glasses exhibit considerable promise as high transparency materials from the UV to the IR(0.2-9 μm), and may offer the best prospects for high performance mid-IR fibers. A critical comparison of the advantages as well as the problems associated with various prospective is given.