ESPnet is an end-to-end speech processing toolkit built on PyTorch, covering a wide range of tasks: automatic speech recognition (ASR), text-to-speech (TTS), speech translation (ST), speech enhancement (SE), speaker recognition, spoken language understanding (SLU), singing voice synthesis (SVS), speech language modeling (SpeechLM), and more. The repository contains both a core Python library (`espnet2/`, `espnet3/`) and a large collection of reproducible recipes (`egs2/`, `egs3/`) for dozens of public corpora and research challenges. The architecture is modular: each task defines its own model, loss, training, and inference via a `Task` class, with abstract base classes for encoders, decoders, frontends, tokenizers, and losses. Configuration is YAML-driven, and the training pipeline uses PyTorch Lightning (in ESPnet3) or a custom trainer (ESPnet2). The system provides CLI tools (`espnet` with subcommands like `transcribe`, `synthesize`, `enhance`, `translate`) and a Python API (`Speech2Text.from_pretrained()`) for inference. It also includes Docker images for deployment and Hugging Face Spaces demos. The repository is hybrid: it is primarily a software framework/library (application) with a strong research character, as evidenced by the extensive recipe collection, benchmark results, and support for state-of-the-art models (Conformer, HuBERT, Whisper, VALL-E). The recipe system follows Kaldi-style data preparation and stage-based pipelines, enabling reproducible experimentation. External dependencies include PyTorch, torchaudio, sentencepiece, and optional components like flash-attn, fairseq, and s3prl. The codebase is actively maintained with CI across multiple OS and Python versions, unit tests, and integration tests.