# Deep Q-Learning [[deep-q-learning]]

<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit4/thumbnail.jpg" alt="Unit 3 thumbnail" width="100%">



In the last unit, we learned our first reinforcement learning algorithm: Q-Learning, **implemented it from scratch**, and trained it in two environments, FrozenLake-v1 ☃️ and Taxi-v3 🚕.

We got excellent results with this simple algorithm, but these environments were relatively simple because the **state space was discrete and small** (16 different states for FrozenLake-v1 and 500 for Taxi-v3). For comparison, the state space in Atari games can **contain \\(10^{9}\\) to \\(10^{11}\\) states**.

But as we'll see, producing and updating a **Q-table can become ineffective in large state space environments.**

So in this unit, **we'll study our first Deep Reinforcement Learning agent**: Deep Q-Learning. Instead of using a Q-table, Deep Q-Learning uses a Neural Network that takes a state and approximates Q-values for each action based on that state.

And **we'll train it to play Space Invaders and other Atari environments using [RL-Zoo](https://github.com/DLR-RM/rl-baselines3-zoo)**, a training framework for RL using Stable-Baselines that provides scripts for training, evaluating agents, tuning hyperparameters, plotting results, and recording videos.

<img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit4/atari-envs.gif" alt="Environments"/>

So let’s get started! 🚀
