Generating object proposals has become a key component of modern object detection pipelines. However, most existing methods generate the object candidates independently of each other. In this paper, we present an approach to co-generating object proposals in multiple images, thus leveraging the collective power of multiple object candidates. In particular, we introduce a deep structured network that jointly predicts the objectness scores and the bounding box locations of multiple object candidates. Our deep structured network consists of a fully-connected Conditional Random Field built on top of a set of deep Convolutional Neural Networks, which learn features to model both the individual object candidates and the similarity between multiple candidates. To train our deep structured network, we develop an end-to-end learning algorithm that, by unrolling the CRF inference procedure, lets us backpropagate the loss gradient throughout the entire structured network. We demonstrate the effectiveness of our approach on two benchmark datasets, showing significant improvement over state-of-the-art object proposal algorithms.