In this seminar I will present the latest research and results on cosmic strings, which are line-like defects which may be formed in spontaneous symmetry breaking phase transitions in the early universe. Such phase transitions may have occurred at grand unification energy scales, and more generally at lower scales. Through their different observational consequences — which I will discuss here — cosmic strings can therefore probe particle physics, and also cosmology, beyond the standard models, and at energy scales much above those of particle accelerators. Being highly relativistic, cosmic strings are sources of gravitational waves (GWs), and a network of cosmic strings formed in the early universe emits GWs throughout its history generating a stochastic gravitational wave background (SGWB). We discuss the shape of this spectrum, depending on the properties of the string network and also the expansion history of the universe, and the constraints which are (and will be) placed by GW detectors. Additionally, cosmic strings produce short bursts of GWs that can be searched for individually in LIGO-Virgo data, and we present the latest results from the O3 run. Finally, we discuss some other advanced and open topics, including how cosmic strings can be a possible component of dark matter.