Flexible and stretchable electronics are opening new opportunities for integration with the human body. In this seminar, I will introduce our recent developments of ultrathin, bio-integrated devices for both wearable and implantable applications. These include a skin-adhesive EMG patch for motion analysis, tissue-adhesive light-emitting devices for cancer therapy, and liquid metal-based microfluidic systems for soft electronics. By matching the mechanics of biological tissues, these platforms aim to achieve comfortable, long-term operation without the need for sutures or rigid components.