One of the major challenges for implementation of solid oxide fuel cells (SOFCs) is the development of suitable sealant materials to separate the air and fuel. Several approaches have been used to achieve the necessary adherence, mechanical integrity and stability, including both rigid seals (no applied load during operation) and compressive seals (load applied to seal during operation). The most common approach is to use rigid glass or glass-ceramic seals, the properties of which can be tailored specifically for use in SOFCs through variation of the glass composition. However, these ceramic materials are inherently brittle, so metallic, metallic-ceramic and ceramic-ceramic composite seals, in both the rigid and compressive configurations, have been developed. The use of multiphase seals allows for improvement in factors, such as wettability, compliance at interfaces and strain relief, to improve the gas-tightness and stability of the seal. In this paper, the different approaches for developing SOFC sealants are reviewed. (c) 2005 Elsevier B.V. All rights reserved.