As one of the biggest social networks in the world, WeChat is innovating the way people acquire needed information, knowledge, and services. We'll present the chatbot development effort made by the WeChat AI team. Both conversational and service-oriented bots are covered. We'll share our vision, our technology, and some good lessons learned while building real-world chatbot products. Especially, we'll demonstrate how deep learning technologies are managed to overcome some hard natural language understanding problems. For example, how the fasttext algorithm is tuned to improve the short question understanding, how to better make use of dialog context by using a recurrent neural network, and how to diversify the dialog response within the encoder-decoder framework. We'll also report our algorithm performance on different GPU cards.