This paper discusses several of these phenomena; hydrolysis, crystallization, and densification by viscous sintering. The discussion of hydrolysis kinetics focuses attention on the reliability of techniques for obtaining kinetic data, presents new data on the hydrolysis of TEOS and models of kinetic behavior, and considers the difficulty of inferring reaction order from single, simple sources of data. The discussion of crystallization and densification focuses on the competition between the two processes and on defining regions of time and temperature where densification can be achieved without significant crystallization, with examples being provided for typical glass-forming systems. -- AATA