  Pseudorandom sequences are used extensively in communications and remote
sensing. Correlation provides one measure of pseudorandomness, and low
correlation is an important factor determining the performance of digital
sequences in applications. We consider the problem of constructing pairs
$(f,g)$ of sequences such that both $f$ and $g$ have low mean square
autocorrelation and $f$ and $g$ have low mean square mutual crosscorrelation.
We focus on aperiodic correlation of binary sequences, and review recent
contributions along with some historical context.
