Seal glass plays a crucial role in solid oxide fuel cell performance and durability. In this review paper, overall composition-structure-property relations of seal glasses are discussed from bulk glass behavior, interfacial interaction, and sealing ability point of view. A seal glass should have a combination of desired thermal, chemical, mechanical, and electrical properties in order to seal cell components and stacks and prevent gas leakage. It must be stable for ∼40,000 h at 500-1000 °C in oxidizing and reducing atmospheres and withstand ∼10,000 thermal cycles between room temperature and cell operating temperature. A SrO-La2O3-Al 2O3-SiO2 based seal glass shows the promise to meet all the desired thermophysical properties, long-term stability, and thermal cycling resistance. In this paper, the most recent advances in the field are discussed along with this glass. Future seal glass research directions for solid oxide fuel cells are also analyzed. © 2010 Elsevier B.V.