This open access book offers a comprehensive and scientifically accurate account of the ecological impact and biological consequences of the Fukushima Daiichi Nuclear Power Plant (FNPP) accident. As a continuation of the previous volume published in 2020, this new volume provides updates and incorporates new findings. Overview introduces the "Dose assessment project for animals affected by the FNPP accident". It addresses the significance of fieldwork and discusses issues and challenges in ensuring the scientific quality of the results obtained. It also addresses the future significance of the project. Part I reviews the released radionuclides and dose assessments reported in the early phase after the accident occurred and compares them with later papers. Focusing on a village affected by the accident, it compares car-borne dose-rate measurements with airborne monitoring data, and predicts the future contamination status. Part II examines the transfer of radioactive cesium from feed to milk, and introduces a monitoring system for radioactive Cs in live cattle and soil/waste. It focuses on creating voxel phantoms and assessing organ doses in wild Japanese macaques. Part III analyzes the impact of the FNPP accident specifically on wild Japanese macaques. It assesses the effect on tooth formation, the cardiovascular system, the lens of the eye, thyroid lesions, and spermatogenesis. Part IV explores the impact of the FNPP accident on various animal species, namely wild butterflies, medaka, and yamame trout, and the assessment of oxidative DNA damage in cattle. Part V investigates experimental effects of 137Cs on silkworms and mice. Part VI examines cellular effects, particularly the alteration of gene expression induced by type B Cs-bearing microparticles, which were first identified following the FNPP accident. It also explores the potential of probiotic bacteria for removing ingested 137Cs. Fifteen years have passed since the accident, and although there have been no reports of significant radiation exposure to the human body, the long-term effects of low-dose radiation on animals and ecosystems are still unknown. Recognizing the importance of preserving knowledge about the FNPP accident for future generations, this book aims to shed light on ongoing research and findings in the field.