  Maximum-length sequences (m-sequences for short) over finite fields are
generated by linear feedback shift registers with primitive characteristic
polynomials. These sequences have nice mathematical structures and good
randomness properties that are favorable in practical applications. During the
past five decades, the crosscorrelation between m-sequences of the same period
has been intensively studied, and a particular research focus has been on
investigating the cross-correlation spectra with few possibles values. In this
chapter we summarize all known results on this topic in the literature and
promote several open problems for future research.
