  Cosmic strings are predicted in many models beyond the Standard Model of
particle physics. In models which admit strings, a network of strings will
inevitably be formed in a phase transition in the early universe and will
persist to the present time. Strings leave behind distinctive features in
cosmology. Searching for these signatures in new observational windows provides
a way to constrain particle physics at the high energy scale and is thus
complementary to searches for new physics at the low energy end, for example at
the LHC. Specifically, I will discuss signatures of cosmic strings in cosmic
microwave background polarization maps and in 21cm redshift surveys.
