Expensive, delicate, and difficult to operate, femtosecond lasers have already won two Nobel Prizes and created multi-billion dollar industries. As these lasers break out of laboratories for use in real-world large-scale applications, the number of people using them increases. This book provides a fresh perspective on femtosecond lasers, discussing how they are soon to become a universal light source, spanning any timescale and generating any wavelength of light. Starting from the basics of light itself, this book presents in an everyday manner, with clear illustrations and without formulas, what makes this class of lasers so versatile and the future of many more applications. Many of the subjects covered in this book are described in plain words for the first time.