Moduli spaces of instantons are a very rich laboratory where physicists and mathematicians enjoy a fruitful interaction. Some of the most exciting corners of this lab are unveiled using supersymmetric gauge theories. It has long been known, for example, that the Higgs branch of certain quiver gauge theories with 8 susy is isomorphic to the moduli space of G-instantons of charge k, where G is any of the classical groups.
In this talk I exploit another avenue, namely that the moduli space of k G instantons is isomorphic to the Coulomb branch of some particular quiver gauge theories in 3d. I will show how we have learnt to calculate  a partition function that counts gauge invariant operators on the chiral ring of the Coulomb branch making use of some special objects called monopole operators. The construction of this partition function allows us to study the moduli space of instantons for any group G, including non-simply laced exceptionals.