There has, in recent years, been a major revival of interest in glass-and glass-ceramic-to-metal seals and coatings for new applications. Experience dictates that many factors need to be taken into consideration in the successful design and manufacture of high-quality seals, particularly if an adequate component lifetime is to be achieved. For example, during their preparation, undesirable reactions may occur between diffusing metal species and glass constituents, and these can lead to the formation of highly localized internal stresses, which can initiate failure of a seal either during manufacture or, more seriously, whilst in service due to the influence of static fatigue. In the case of high-temperature systems, reactions under hostile operating conditions also need to be taken into consideration. In this review, the factors learnt from past experience that influence the formation and lifetime behaviour of glass and glass-ceramic/metal systems are briefly introduced, and their relevance to the newer applications including solid oxide fuel cell sealants and coatings on titanium for biomedical applications is discussed.