As mentioned in the previous chapter, the second neural boom, Second neural boom like the first neural boom, First neural boom also entered the winter period. The trigger to emerge from that long winter period was deep learning, which evoked another neural boom. What makes this boom different from previous ones is that high expectations are placed on its high practicality. Deep learning has solved various problems caused by increasing the number of layers in a neural network, and neural network research has made unprecedented progress. Among them, convolutional neural networks are the core technology of deep learning. Therefore, in this chapter, we focus on convolutional neural networks and discuss them emphatically.