Attempts to decouple band gap from strain-engineering in group IV materials motivated a significant effort to develop ternary SiGeSn alloys. These grow either directly on Si (100) or on GeSn- and Ge-buffered Si substrates, remain stable at temperatures beyond 800°C (depending on composition), and display intriguing electronic and transport properties. In particular, the complete decoupling of electronic structure and lattice constant was demonstrated in a specific family of SiGeSn alloys lattice-matched to Ge  and transport measurements in n- and p-type analogs reveal mobilities comparable to those in elemental Ge. Combined with novel CVD approaches to the growth of binary GeSn alloys  as well as superior quality Ge films on Si substrates , these materials represent an entire new class of IR semiconductors with the potential to revolutionize the field of group-IV materials. The purpose of this paper is to review the preparation and properties of SiGeSn alloys and discuss their potential for photonic applications. The two-dimensional compositional space of this system as well as the many possible lattice matched and un-matched combinations of ternary, binary, and elemental group-IV semiconductors provide unprecedented flexibility to further develop and optimize the basic properties of these materials for optoelectronic, thermoelectricity and potentially photovoltaics.