Micro-milling is a precision milling technology where the cutting parameters are in micro scale. It has been increasingly applied to modern industry, from aerospace to bioengineering. Tool condition monitoring (TCM) in micro milling poses new challenges compared to conventional CNC machining, due to the high tool wear rate and high precision requirement associated with the features at micro-level. In this book, a generic noise-robust system is developed for the micro-milling tool condition monitoring. Mathematical tools such wavelet analysis and independent component analysis (ICA) have been applied to analyze the cutting force associated with different tool conditions. Continuous Hidden Markov models (HMMs) are adapted to model the tool wearing process and estimate the tool states based on the force features. Experimental studies on the tool state estimation in the micro-milling of pure copper and steel illustrate the effectiveness these approaches. This book serves as a valuable reference to the graduate students and the engineers engaged in the research in precision manufacturing, automation and control, and signal processing.