This book constitutes the refereed post-conference proceedings of the Third International Conference on Deep Learning Theory and Applications, De LTA 2022, held in Lisbon, Portugal, during January 17-18, 2022.The 6 full papers included in this book were carefully reviewed and selected from 36 submissions. They present recent research on machine learning and artificial intelligence in real-world applications such as computer vision, information retrieval and summarization from structured and unstructured multimodal data sources, natural language understanding and translation, and many other application domains.