Partial conservation of seniority in nuclei

8 pages, 2 figures. Presented at the 17th Nuclear Physics Conference "Marie and Pierre Curie" on " Symmetry and Symmetry Breaking in Nuclear Physics", Kazimierz Dolny, 22-26 september 2010, Poland. Accepted for publication in International Journal of Modern Physics E.A review is given of the relation between pairing, quasi-spin algebras and seniority. The former two concepts are closely connected, the relation being that the quasi-spin formalism allows an efficient solution of the pairing problem. %with intrinsic degrees of freedom such as isospin. Seniority is of much wider applicability than either pairing or quasi-spin and applications can even be extended to encompass the notion of partial symmetry. A recent application of partial conservation of seniority and its importance for nuclear isomers is discussed