This document is a syllabus for a Deep Reinforcement Learning course offered at Harvard Extension School in Spring 2021. The course will be taught online and cover topics such as Markov Decision Processes, dynamic programming, Monte Carlo methods, temporal-difference learning, deep learning, value-based deep RL, policy-based deep RL and model-based deep RL. Students will complete homework assignments, quizzes, a midterm exam and final exam in Python. The course aims to provide students with skills in building optimal neural networks for reinforcement learning tasks.