Galaxy groups and clusters are cosmic giants. They are the largest observable virialised objects that have materialised from the initial perturbations in the early Universe. These systems comprise of not only galaxies, but also hot gas and dark matter. They are ideal astrophysical laboratories to study the matter distribution of the Universe and cluster physics whilst their distribution and evolution can be used constrain cosmological parameters. Clusters are the ultimate test for the structure formation paradigm. However, for this to be achieved requires knowledge of their mass which is a particularly challenging task since there are no ‘cosmic scales’ to directly measure the masses of these objects. Groups and clusters are massive enough to gravitationally influence light emitted from background galaxies, an effect known as gravitational lensing. Its mass can be inferred from the strength of the weak lensing signal and is only dependent on the gravitational potential well depth. However, its limitations arise from systematic uncertainties of shape measurement, photometric redshift and shallow survey depth. This thesis concerns constraining accurate and precise cluster mass estimates of low mass groups and poor clusters, and testing the limits that can be achieved with current noisy, ground-based data.