The bifurcation function for an elliptic boundary value problem is a vector field B(ω) on R d whose zeros are in a one-to-one correspondence with the solutions of the boundary value problem. Finite element approximations of the boundary value problem are shown to give rise to an approximate bifurcation function B h (ω), which is also a vector field on R d . Estimates of the difference B(ω) − B h (ω) are derived, and methods for computing B h (ω) are discussed.