Specializations of indecomposable polynomials

We address some questions concerning indecomposable polynomials and their behaviour under specialization. For instance we give a bound on a prime p for the reduction modulo p of an indecomposable polynomial ${P(x)\in {\mathbb{Z}}x]}$ to remain indecomposable. We also obtain a Hilbert like result for indecomposability: if f(t ₁, . . . , t _r , x) is an indecomposable polynomial in several variables with coefficients in a field of characteristic p?=?0 or p?>?deg(f), then the one variable specialized polynomial ${f(t_1^\ast+\alpha_1^\ast x,\ldots,t_r^\ast+\alpha_r^\ast x,x)}$ is indecomposable for all ${(t_1^\ast, \ldots, t_r^\ast, \alpha_1^\ast, \ldots,\alpha_r^\ast)\in \overline k^{2r}}$ outside a proper Zariski closed subset.