Directed percolation (DP) is the paradigmatic absorbing-state phase transition. Bonds open with probability p in the time direction only. At p_c ≈ 0.6447 (1+1D square lattice), a second-order transition occurs with exponents β ≈ 0.2765, ν_∥ ≈ 1.734. The field theory is Reggeon field theory (Gribov–Migdal).