Monoclonal antibodies are an important class of therapeutic agent that are in widespread use for the effective treatment of many human diseases. We have used a number of mass spectrometers (Synapt G2 and OrbiTrap Exactive Plus extended mass range [EMR]) and ion mobility instruments (Synapt G1 modified to an radio frequency [RF]-confining drift cell and a Synapt G2 travelling wave system) to characterise the humanised IgG1k NIST monoclonal antibody molecule under native-MS and buffer conditions. On both the Synapt G2 and the OrbiTrap instrumentation, charge state distributions are very similar, and all major glycoforms were resolved on all observable charge states; however, only on the OrbiTrap instrument are the glycoforms fully resolved to baseline. Ion mobility measurements were made in both helium and nitrogen drift gases on an RF-confining drift cell device with derived collision cross-section values for charge states +21 to +26 range from 6696 2 to 6892 2 in helium and 7223 2 to 7403 2 in nitrogen, respectively. This small but gradual increase in collision cross section with increasing charge can be attributed to a combination of increasing ion-induced dipole interaction between the charged protein and the neutral drift gas and the enlargement of the protein due to the repulsion of the surface charges. The higher charge states (+27 to +29) show a significant amount of gas-phase unfolding, evident by increased collision cross-section values and bimodal ion mobility arrival times. Collision cross sections measured on a travelling wave device (in nitrogen) were consistent with the mobility measurements made in nitrogen on the RF-confining drift cell device. Molecular dynamic simulations on the theoretically generated NIST monoclonal antibody (NISTmAb) coordinate structure indicate that the gas-phase structure undergoes a significant (up to 40%) amount of compaction. Theoretical collision cross-section calculations on the optimised molecular dynamic-derived NISTmAb structure are consistent with both helium and nitrogen instrument-derived collision cross-section values. Finally, collision-induced unfolding experiments also were performed on the +26 charge of the NISTmAb and could potentially be used as a means of providing structural information in addition to a single, and potentially limiting, gas phase-derived collision cross-section measurement.