Abstract: In this talk I will discuss a construction of boundary vertex operator algebras (VOA) in topological twists of 3d N=4 quantum field theories. This construction is a useful way to study the 3d mirror symmetry of the A and B twists of such a theory. In particular, it is conjectured that the associated variety of the A-twist boundary VOA is the Higgs branch of the full physical theory and the derived endomorphism algebra is the Coulomb branch algebra. I will discuss recent work in collaboration with Andrea Ferrari in which we proved the Higgs branch conjecture for U(1)-gauge theory.