β-functions and the exact renormalization group

We relate β-functions to the flow of relevant couplings in the exact renormalization group. The specific case of a cutoff λΦ4 theory in four dimensions is discussed in detail. The underlying idea of convergence of the flow of effective lagrangians is developed to identify the β-functions. A perturbative calculation of the β-functions using the exact flow equations is sketched. The analysis may be extended to any system with a cutoff. (orig.)