This article reviews fiber-based wearable electronics, focusing on materials, fabrication, devices, and applications. Fiber-based structures are ideal for wearable electronics due to their lightweight, flexible, and conformable nature. These structures are typically manufactured using established textile processing technologies. Advances in nanotechnology have enabled the integration of electronic functions directly onto fibers, which are typically 1-50 microns thick. However, integrating electronic functions into porous, deformable fiber assemblies and maintaining them during wear remains a challenge. The review critically examines current state-of-the-art materials, fabrication techniques, and device designs for fiber-based wearable electronics, as well as their applications in healthcare, environmental monitoring, displays, energy conversion, and communication. It also discusses the performance requirements of these devices, particularly the relationship between materials, fiber/textile structures, and electronic/mechanical functionalities. The review highlights the limitations of current materials and devices in terms of manufacturability, performance, and scientific understanding, and suggests areas for improvement before widespread adoption. Conductive materials such as conducting polymers, carbon-based materials, and metallic nanoparticles/nanowires are discussed for their potential in fiber-based electronics. Fabrication technologies, including surface mounting, conductive nano-coating, and self-organizing methods, are reviewed for their role in creating wearable electronic devices. The article also covers e-components, devices, and applications, including fiber transistors, fabric antennas, electric connectors, and sensors. It emphasizes the importance of mechanical and electrical stability, fatigue resistance, and the integration of electronic functions into textiles for practical wearable applications. The review concludes with a discussion on the challenges and future directions for fiber-based wearable electronics.This article reviews fiber-based wearable electronics, focusing on materials, fabrication, devices, and applications. Fiber-based structures are ideal for wearable electronics due to their lightweight, flexible, and conformable nature. These structures are typically manufactured using established textile processing technologies. Advances in nanotechnology have enabled the integration of electronic functions directly onto fibers, which are typically 1-50 microns thick. However, integrating electronic functions into porous, deformable fiber assemblies and maintaining them during wear remains a challenge. The review critically examines current state-of-the-art materials, fabrication techniques, and device designs for fiber-based wearable electronics, as well as their applications in healthcare, environmental monitoring, displays, energy conversion, and communication. It also discusses the performance requirements of these devices, particularly the relationship between materials, fiber/textile structures, and electronic/mechanical functionalities. The review highlights the limitations of current materials and devices in terms of manufacturability, performance, and scientific understanding, and suggests areas for improvement before widespread adoption. Conductive materials such as conducting polymers, carbon-based materials, and metallic nanoparticles/nanowires are discussed for their potential in fiber-based electronics. Fabrication technologies, including surface mounting, conductive nano-coating, and self-organizing methods, are reviewed for their role in creating wearable electronic devices. The article also covers e-components, devices, and applications, including fiber transistors, fabric antennas, electric connectors, and sensors. It emphasizes the importance of mechanical and electrical stability, fatigue resistance, and the integration of electronic functions into textiles for practical wearable applications. The review concludes with a discussion on the challenges and future directions for fiber-based wearable electronics.