We present first-principles calculations of structural, electronic, magnetic, and optical properties of zigzag-oriented silicene nanoribbons, which, being endowed with spin-polarized edge states, are promising candidates as building blocks of future spintronic devices. The minimal width for a structurally stable planar structure having zigzag edges corresponds to a 4-chain ribbon, whose ground state presents antiferromagnetically coupled spin-polarized edges, and a lattice parameter along the nanoribbon axis contracted (∼ 5%) with respect to the bulk value. Starting from the dependence of structural and electronic properties on the ribbon width, we present theoretical predictions for the optical spectra of narrow nanoribbons, in which excitonic effects are relevant due to the confinement in a quasi-one-dimensional structure. Especially for light polarized parallel to the ribbon axis, we find significant differences in the …