The renormalization group (RG) flow describes the change of effective theories as the momentum cutoff is lowered. However, it is often hard to compute the exact effective action because operators composed of arbitrary numbers of fields and space derivatives are generated under the exact RG flow. This difficulty is alleviated in quantum RG, which is an exact reformulation of the Wilsonian RG. It significantly reduces the number of operators that need to be included as the full RG flow is projected onto a measure zero subspace of couplings while the couplings in the subspace are promoted to dynamical variables. In this talk, we review the basic idea of quantum RG and present the exact effective action of the large-N Wilson-Fisher fixed point obtained from quantum RG. Below four dimensions, the exact effective action is a transcendental function of two leading scaling operators with infinitely many derivatives.