Given a field KK and n>1n>1, we say that a polynomial f∈K[x]f∈K[x] has newly reducible nnth iterate over KK if fn−1fn−1 is irreducible over KK, but fnfn is not (here fifi denotes the iith iterate of ff). We pose the problem of characterizing, for given d,n>1d,n>1, fields KK such that there exists f∈K[x]f∈K[x] of degree dd with newly reducible nnth iterate, and the similar problem for fields admitting infinitely many such ff. We give results in the cases (d,n)∈{(2,3),(3,2),(4,2)}(d,n)∈{(2,3),(3,2),(4,2)} as well as for (d,2)(d,2) when d≡2mod4d≡2mod4. In particular, we show that for all these (d,n)(d,n) pairs, there are infinitely many monic f∈ℤ[x] of degree d with newly reducible nth iterate over ℚ. Curiously, the minimal polynomial x2−x−1 of the golden ratio is one example of f∈ℤ[x] with newly reducible third iterate; very few other examples have small coefficients. Our investigations prompt a number of conjectures and open questions.