Spin-based electronics, often referred to as "spintronics", is a research field of intense current interest, which aims to develop novel sensor, memory and logic devices by manipulating the spin states of electrons or holes in semiconducting materials. This talk will focus on electrical spin injection into semiconductors, which is a prerequisite for spintronics and, in particular, on tunnel based spin injectors operable above room temperature. Two types of spin injectors, formed from 3d transition metal ferromagnets and oxide tunnel barriers, are discussed: a three-terminal magnetic tunnel transistor (MTT) injector )@footnote 1,2@ and a two-terminal magnetic tunnel injector.@footnote 3@ A two terminal tunnel spin injector, comprised of CoFe/MgO(100), is shown to give more than 50% spin polarized current within GaAs (100) heterostructures at room temperature.@footnote 3@ The spin polarization of the injected current is inferred from the electroluminescence polarization (ELP) from GaAs/AlGaAs quantum well detectors. The high polarization values are consistent with giant values of tunneling spin polarization (TSP) measured in superconducting tunneling junctions in which the CoFe/MgO layers are highly textured (100). Recently, we have reported TSP values of up to 85% (at 0.25 K) and tunneling magnetoresistance values (TMR) of >220% in CoFe/MgO(100) magnetic tunnel junctions at room temperature.@footnote 4@ Such high values of TSP and TMR, previously only obtained at low temperatures using half-metallic ferromagnets, promise the development of new families of spintronic devices operating at room temperature based on conventional ferromagnets. * work carried out in collaboration with X. Jiang, R. Wang, C. Kaiser, R. Shelby, R. MacFarlane, G. Solomon and J. Harris. @FootnoteText@ @footnote 1@S. van Dijken et al., Appl. Phys. Lett. 83, 951 (2003). @footnote 2@ X. Jiang, et al., Phys. Rev. Lett. 90, 256603 (2003). @footnote 3@X. Jiang et al, Phys. Rev. Lett. 94, 056601 (2005). @footnote 4@S. S. P. Parkin, et al., Nature Mater. 3, 862 (2004).