  In this paper, we prove two unique continuation results for second order
elliptic equations with Robin boundary conditions on $C^{1,1}$ domains. The
first one is a sharp vanishing order estimate of Robin problems with Lipschitz
coefficients and differentiable, sign-changing potentials. This generalizes the
result for the "Robin eigenfunctions" in [26], which deals with the case with
constant potentials. The second result is a unique continuation result from the
boundary -- any non-trivial solution cannot vanish at infinite order from the
boundary or vanish on an open subset on the boundary. Such result generalizes
the one in [1] for the Laplace equation on $C^{1,1}$ domains with zero Neumann
boundary conditions.
