Deep Learning, Ian Goodfellow, Yoshua Bengio, and Aaron Courville, 2016 (MIT Press)DOI: 10.7551/mitpress/9780262035613.001.0001 - A fundamental textbook that provides extensive theoretical background on supervised learning, neural network architectures, backpropagation, loss functions, and optimization algorithms.
Neural Networks and Deep Learning, Michael A. Nielsen, 2015 (Determination Press) - An accessible online book offering clear explanations of neural network mechanics, with a particular focus on how backpropagation enables networks to learn.