A survey is presented of the different aspects of gelation in polymeric materials with the purpose of highlighting the basic processes and underlying principles that can lead to gel formation. It is illustrated with specific examples, largely arising from the author's own experiences or associations, chosen so as to provide as representative a sampling of the wide-ranging subject area as possible. Within a wider overall framework emphasis is given to physical gelation, especially where this arises through phase separation. In the latter respect the hierarchical relation of both the resulting structures and the underlying thermodynamic stabilities, or rather metastabilities, is given prominence, together with its further reaching implications which can extend also beyond the confines of the subject of gels.