A convex-polynomial is a convex combination of the monomials {1, x, x 2 , . . .}. This paper establishes that the convex-polynomials on R are dense in L p (µ) and weak * dense in L ∞ (µ), precisely when µ([−1, ∞)) = 0.It is shown that the convex-polynomials are dense in C(K) precisely whenwhere K is a compact subset of the real line. Moreover, the closure of the convex-polynomials on [−1, b] are shown to be the functions that have a convex-power series representation.A continuous linear operator T on a locally convex space X is convex-cyclic if there is a vector x ∈ X such that the convex hull of the orbit of x is dense in X. The above results characterize which multiplication operators on various real Banach spaces are convex-cyclic. It is shown for certain multiplication operators that every closed invariant convex set is a closed invariant subspace.