Title: "Collective Stochastic Resonance". Abstract: Using a stochastic model of neural networks, we investigate analytically and numerically response of neural networks on weak time dependent stimuli in the presence of noise. We propose a new mechanism of stochastic resonance, so called "collective stochastic resonance". It occurs in neural networks which undergo a transition from a state with short-range spatio-temporal correlations between neurons to a state with network oscillations. We find that dynamical stochastic resonance emerges as the precursor of global oscillations. It increases the output signal-to-noise ratio and improves the recognition of weak sensory stimuli. We show that a modular organization of neural networks can improve the reliability of detection of weak signals.