Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press) - A comprehensive textbook that covers the fundamental machine learning concepts, including overfitting, generalization, and the bias-variance trade-off, within the context of deep neural networks.
The Elements of Statistical Learning: Data Mining, Inference, and Prediction, Trevor Hastie, Robert Tibshirani, and Jerome Friedman, 2009 (Springer) - A classic reference in statistical learning, offering a rigorous theoretical background on model assessment, selection, and the bias-variance problem, which is central to understanding overfitting.
Machine Learning, Andrew Ng, 2016Coursera (DeepLearning.AI and Stanford Online) - An widely recognized introductory online course that clearly explains the concepts of overfitting, underfitting, and the practical methods for detecting them using training and validation sets.