Domain Randomization is arguably one of the most influential techniques at the intersection of simulation and real-world robotics. Developed by OpenAI and presented at IROS 2017, the method addresses the reality gap by deliberately randomizing non-essential properties of the simulator during training. Rather than making the simulation look photorealistic, the idea is to make the neural network invariant to visual nuisance factors—such as textures, lighting, camera pose, and object colors—by exposing it to a sufficiently diverse distribution of appearances. The canonical experiment in the paper involves a robotic arm learning to localize and pick a small colored cube from a table. Instead of rendering the scene with realistic textures, the training environment randomizes every visual attribute: background images, cube texture, light positions, camera angle, and even occlusion patterns. At test time, the same neural-network policy, with no domain-specific fine-tuning, is deployed on a physical robot and successfully grasps the real cube. This demonstrated that extreme visual randomization could serve as a form of implicit domain adaptation. Mathematically, the insight is that if the support of the randomized training distribution covers the real-world appearance, then a sufficiently capacity-constrained network will learn features robust to all nuisance variations. Since 2017, domain randomization has become a standard preprocessing step in vision-based sim-to-real pipelines. Extensive follow-up work has expanded it to dynamics randomization (varying mass, friction, and actuator gains), shape randomization (domain randomization on geometry), and even adversarial variants such as learning-to-simulate. For modern robotics researchers, domain randomization remains an essential baseline approach when transferring perception and policy networks from synthetic data to hardware. The original paper is short, clearly written, and highly reproducible in MuJoCo or PyBullet. Its conceptual clarity makes it an ideal reference in sim-to-real courses and tutorials, and its influence can be traced directly to the wide adoption of synthetic training in manipulation and navigation research that followed.