Preface.- Acknowledgements.- Introduction.- Gravitational Waves and the Quest for their Direct Detection.- Quantum Optics and Light.- Quantum Noise in Gravitational -Wave Detectors and Applied Squeezed States.- Squeezed State Generation for Gravitational-wave Detection.- The Doubly Resonant, Travelling- Wave Squeezed Light Source.- Backscatter Tolerance of a travelling-wave Optical Parametric Oscillator.- Overview of the LIGO Squeezed Light Injection Experiment.- Squeezing-enhancement of a 4km LIGO gravitational-wave detector.- Backscattered-light Impact in a Squeezing-enhanced Gravitational-Wave Detector.- Results Summary, Recommendations and Future Work.- Quantum noise and squeezing in Dual-recycled Michelson Interferometers.- Initial analysis and repair of the Enhanced LIGO H1 Output Mode Cleaner.- Supplementary Information for the Backscatter-light Experiments at LIGO.