  This paper overviews the behavior of the end-chain spins of linear chain
systems possessing a Haldane gap. The physical properties of the end-chain
spins are described by reviewing the results obtained primarily with materials
known as NENP, Ni(C2H8N2)2NO2(ClO4), and NINAZ, Ni(C3H10N2)2N3(ClO4).
