  We review from a theoretical perspective the emerging field of spintronics
where active control of spin transport and dynamics in electronic materials may
provide novel device application possibilities. In particular, we discuss the
quantum mechanical principles underlying spintronics applications, emphasizing
the formidable challenges involving spin decoherence and spin injection facing
any eventual device fabrication. We provide a critical assessment of the
current status of the field with special attention to possible device
applications.
