Detectron2 is a production-grade, modular computer vision library from Facebook AI Research, designed for object detection, instance/semantic/panoptic segmentation, keypoint detection, and dense pose estimation. It provides a full training and inference pipeline with configurable architectures (Mask R-CNN, RetinaNet, FCOS, etc.), a flexible configuration system (CfgNode and LazyConfig), extensive data loading and augmentation, evaluation metrics for standard benchmarks (COCO, LVIS, Cityscapes), and deployment support via TorchScript and ONNX. The codebase is organized around registries and configurable classes, enabling easy extension. It also includes several research projects (DensePose, PointRend, DeepLab, etc.) as subdirectories, demonstrating its use as a research platform. While the core is well-maintained, some legacy features (Caffe2 export, deprecated LR schedulers) and project-specific code introduce moderate technical drift.