The onset of magnetism and the magnetic propreties of concentrated substitutional ternary alloys A(Fe 1− x B x ) 2 (A = Y, Zr, U; B = Mn, Co, Ni and Al), Y 2(Ni 1− x Co x ) 7, Y(Ni 1− x Co x ) 3, Y 6(Fe 1− x Mn x ) 23 and Ti(Fe 1− x Co x ) as well as the amorphous alloy system (Fe 1− x Ni x ) 77Si 10B 13 are discussed in terms of homogeneous and heterogeneous models based on the Stoner-, Edwards- Wohlfa arth- and the Landau theory of phase transitions of second order. For a detailed comparison of the nine ternary systems A(Fe, B) 2 (A = Y, Zr, U; B = Mn, Co, Al) we refer to a following paper. From the results obtained on alloying UNi 2 with Fe, Co and Cu we propose that the magnetic moment of UNi 2—contrary to UFe 2—resides mainly on U rather than on the Ni site. The appearance of magnetism in YNi x compounds by either changing the Y : Ni ratio or substituting Ni by Co in YNi 3 and Y 2Ni 7 is mainly attributed to band effects for which a schematic N( E) curve is proposed. The breakdown of long-range magnetic order in Y 6(Fe, Mn) 23 seems to be caused by a lack of delocalized electrons and a preferential site occupation of Mn and Fe. The magnetic properties of Ti(Fe 1− x Co x ) change from an itinerant to a localized moment behaviour above and below x = 0.5 due to the occurrence of Fe antistructure atoms which drive the onset of long-range magnetic order. The occurrence of magnetism in amorphous alloys compared with that of crystalline alloys with a high degree of disorder may be characterized in a similar way.