The fully nonlinear governing equations for spin 1 2 quantum plasmas are presented. Starting from the Pauli equation, the relevant plasma equations are derived, and it is shown that nontrivial quantum spin couplings arise, enabling studies of the combined collective and spin dynamics. The linear response of the quantum plasma in an electron-ion system is obtained and analyzed. Applications of the theory to solid state and astrophysical systems as well as dusty plasmas are pointed out.PACS numbers: 52.27.-h, 52.27. Gr, 67.57.Lm There is currently a great deal of interest in investigating collective plasma modes [1,2,3,4,5,6,7,8] in quantum plasmas, as such plasmas could be of relevance in nano-scale electro-mechanical systems [9,10,11], in microplasmas and dense laser-plasmas [12], and laser interactions with atomic systems [13,14]. For example, Refs.[1] and [3,4,5] used quantum transport models in order to derive modified dispersion relations for Langmuir and ion-acoustic waves, while Shukla & Stenflo [15] ionvestigated drift modes in nonuniform quantum magnetoplasmas. Moreover, it is known that cold quantum plasmas can support new dust modes [16,17]. In Ref.[8] it was shown that electron quantum plasmas could support highly stable dark solitons and vortices. Further examples of quantum plasmas and the range of validity of their descriptions has been discussed recently in Ref. [18]. The above studies of quantum plasmas have used models based on the Schrödinger description of the electron. It is expected that new and possible important effects could appear as further quantum effects are incorporated in models describing the quantum plasma particles. The coupling of spin to classical motion has attracted interest in the literature (see, e.g., [19,20,21,22,23,24,25,26,27,28,29,30,31]). Much work has been done concerning single particle spin effects in external field configurations, such as intense laser fields [22,23,24,25,26,27], and the possible experimental signatures thereof. However, there have also been interest in excitations of collective modes in spin systems, such as spin waves, in a wide scientific community. For example, in Refs. [19,20,21] hydrodynamical models including spin was presented, and further theory concerning spin, angular momentum, and the forces related to spin was discussed in Refs. [29] and [30]. Moreover, spin waves in spinor Bose condensates has recently been discussed in, e.g., Ref. [31]. The treatment of charged particles and plasmas using quantum theory has received attention in astrophysical settings, especially in strongly mag- * Electronic address: mattias.marklund@physics.umu.se † Electronic address: gert.brodin@physics.umu.se netized environments [32,33]. For example, effects of quantum field theory on the linear response of an electron gas has been analyzed [34], results concerning the spin-dependence of cyclotron decay on strong magnetic fields has been presented [35], and the propagation of quantum electrodynamical waves in strongly magnetized plasmas has been considered ...