The factors which can influence the performance and reliability of the interconnection system for solid-state components in hybrid integrated circuits are examined. The main emphasis is on materials that have received most attention in the tantalum film and silicon technologies in the Bell System. However, other materials that are being used are discussed. The interrelation of various factors in choosing an interconnection system is discussed. These factors include the composition of the materials, the methods of depositing various metals, and the properties of the substrates. Among the properties of the materials that are considered. emphasis is laid on environmental stability. The results of environmental tests on conductors and thin-film resistors under high-humidity conditions are reported. Some results on the use of silicone rubber as an encapsulant indicate this material is effective in reducing degradative action on hybrid circuits.