Binary Neural Networks: A Survey

•We summarize the binary neural network methods and categorize them into the naive binarization and the optimized binarization.•The binary neural networks are mainly optimized using techniques including minimizing quantization error, improving the loss function, and reducing the gradient error.•We also discuss the hardware-friendly methods and the useful tricks of training binary neural networks.•We present the common datasets and network structures of evaluation, and compare the performance on different tasks.•We conclude and point out the future research trends.