This book looks at the physics of electronic fluctuations (noise) in solids. The author emphasizes many fundamental experiments that have become classics: physical mechanisms of fluctuations, and the nature and magnitude of noise. He also includes the most comprehensive and complete review of flicker (1/f) noise in the literature. It will be useful to graduate students and researchers in physics and electronic engineering, and especially those carrying out research in the fields of noise phenomena and highly sensitive electronic devices--detectors, electronic devices for low-noise amplifiers, and quantum magnetometers (SQUIDS).