Neural Networks and Deep Learning is a free online book. The book will teach you about:
Neural networks, a beautiful biologically-inspired programming paradigm which enables a computer to learn from observational data
Deep learning, a powerful set of techniques for learning in neural networks
Neural networks and deep learning currently provide the best solutions to many problems in image recognition, speech recognition, and natural language processing. This book will teach you the core concepts behind neural networks and deep learning.
The book is currently an incomplete beta draft. More chapters will be added over the coming months. For now, you can:
Read Chapter 1, which explains how neural networks can learn to recognize handwriting
Read Chapter 2, which explains backpropagation, the most important algorithm used to learn in neural networks.
Read Chapter 3, which explains many techniques which can be used to improve the performance of backpropagation.
Read Chapter 4, which explains why neural networks can compute any function.