Since 1993 Fraunhofer IKTS is developing Solid-oxide-fuel-cell (SOFC) components and stacks. At SOFC stack development different fields of cells, glass seals, interconnects and contacting as well as design, simulation, assembly and quality assurance have to be merged together. The SOFC stacks are the heart of every SOFC or SOEC (high temperature electrolysis) system and have to be proper integrated to a successful operation for a wide variety of applications (see figure Application of CFY stacks MK35x). With the work at several projects scientific knowledge were raised for design and construction of planar SOFC stacks as well as their integration into systems for SOFC, SOEC and reversible operation (rSOC). The development focus is set to lowering price and degradation rate to pave the way to commercialize the SOC technology. Fraunhofer IKTS sets test standards (e.g. long-term, accelerated and cycling tests) of components, stacks and stack modules.