Magnetic / semiconductor heterostructures offer many exciting opportunities for spintronic applications, ranging from hybrid device structures to direct spin injection. We describe here recent results of each. We have fabricated hybrid logic cells which provide fully reprogrammable, nonvolatile logic operation by combining GMR elements with InAs/AlSb/GaSb resonant interband tunneling diodes (RITDs). Such programmable cells allow the use of a low component count common building block for multiple logic functions, and combine the low power, high speed operation of the RITD with the nonvolatile character of GMR elements. Electrical spin injection and transport in semiconductors is another promising avenue to add spin-dependent functionality to the many attractive device properties of semiconductor compounds -- it provides a very simple means of spin injection, and significantly broadens the potential for practical applications.@footnote 1-3@ We have recently demonstrated highly efficient electrical injection of spin-polarized electrons into a AlGaAs/GaAs-based quantum well LED heterostructure using a non-lattice matched epilayer of the semimagnetic semiconductor ZnMnSe as the spin injecting contact. The electroluminescence (EL) from the quantum well is strongly polarized, and provides a quantitative measure of spin injection across the ZnMnSe/AlGaAs interface. Other components of the EL spectrum exhibit little polarization, and provide insight into spin relaxation mechanisms. Ferromagnetic semiconductors provide an ideal contact for electrical spin injection and/or transport -- they are closely matched in conductivity and band structure, and require no large magnetic bias field to produce spin polarized carriers. Several candidate materials will be discussed. ** Supported by ONR and the DARPA SPINS program.@FootnoteText@ @footnote 1@ B.T. Jonker et al, submitted. @footnote 2@ R. Fiederling et al, Nature 402, 787 (1999) @footnote 3@ Y. Ohno et al, ibid p. 790.