It was known that the worldvolume of multiple M2-branes is described by 3D supersymmetric Chern-Simons theory (known as ABJM theory). After moving to the grand canonical ensemble, it was found in our previous works that the vacuum expectation values of half-BPS Wilson loops in the ABJM theory satisfy Giambelli relations and Jacobi-Trudi relations, which imply integrability directly. To investigate the integrable structure, we further defined two-point functions in ABJM matrix model and identified the structure as 2D Toda lattice hierarchy. In this talk I will give an overview of the recent progress on integrability in the ABJM theory.