This chapter presents an alternative method of injecting spin-polarized electrons into a nonmagnetic semiconductor through photoexcitation. This method uses circularly-polarized light, whose energy needs to be the same as, or slightly larger than, the semiconductor band-gap, to excite spin-polarized electrons. This process will introduce a spin-polarized electron-hole pair, which can be detected as electrical signals. Such an optically induced spin-polarized current can only be generated in a direct band-gap semiconductor due to the selection rule described in the following sections. This introduction of circularly polarized light can also be used for spin-polarized scanning tunnelling microscopy.