Abstract: Methods, systems, and apparatus, including computer programs encoded on computer storage media, for determining neural network architectures. One of the methods includes receiving training data for training a task neural network to perform a particular machine learning task; and selecting, from a space of possible architectures, an architecture for the task neural network, wherein the space of possible architectures is represented as a graph of nodes connected by edges, each node in the graph representing a decision point in selecting the architecture and each edge in the graph representing an action.