A new low-latitude ionospheric model has been developed at the Naval Research Laboratory: Sami2 is Another Model of the Ionosphere (SAMI2). SAMI2 treats the dynamic plasma and chemical evolution of seven ion species (H+, He+, N+, O+, N2+, NO+, and O2+) in the altitude range ~100 km to several thousand kilometers. The ion continuity and momentum equations are solved for all seven species; the temperature equation is solved for H+, He+, O+, and the electrons. SAMI2 models the plasma along the Earth's dipole field from hemisphere to hemisphere, includes the E¿B drift of a flux tube (both in altitude and in longitude), and includes ion inertia in the ion momentum equation for motion along the dipole field line. The final point is relevant for plasma dynamics at very high altitudes where ion inertia can be important. For example, we have found that ion sound waves, which are supported by ion inertia, may be generated in the topside ionosphere (>1000 km) at sunrise and sunset [Huba et al., 2000b>. The neutral species are specified using the Mass Spectrometer Incoherent Scatter model (MSIS86) and the Horizontal Wind Model (HWM93). In this paper we describe in detail the SAMI2 model and present representative results from the model. ¿ 2000 American Geophysical Union