Gamma-ray bursts’ (GRBs) jets are launched from a compact object and travel large distances before dissipating their energy in the form of electromagnetic radiation. GRB jets must break out from their surrounding medium and in this process they are imprinted with a jet “structure,” with jet energy decreasing with increasing angle from the jet axis. We will discuss how the study of the jet breakout has been important in understanding the GRB progenitor properties (of both long and short GRBs). We will also discuss how the study of the jet structure using recent realistic 3D GRMHD simulations of short GRB jets has allowed us to understand the observed multi-wavelength emission of the neutron star merger event GW170817. The study of GRB jets continues to be of paramount importance in multi-messenger astronomy as we expect the detection of gravitational waves from other neutron star mergers in the near future.