The Advanced LIGO gravitational wave detectors are second-generation instruments designed for the two LIGO observatories in Hanford, WA and Livingston, LA. They are identical Michelson interferometers with 4 km long arms, featuring Fabry-Perot cavities and power recycling to enhance sensitivity. Advanced LIGO improves strain sensitivity by a factor of 10 over initial LIGO, extending the low-frequency sensitivity to 10 Hz. It uses signal recycling to improve frequency response and includes better seismic isolation and test mass suspensions. Data collection began in mid-2015. Advanced LIGO replaces all interferometer components with improved technologies, including larger test masses and better mirror coatings. A third interferometer is planned for India. The detectors are expected to detect dozens of compact binary coalescence sources per year. The interferometer uses a multi-stage Nd:YAG laser with up to 180 W output. The optical configuration includes a 50/50 beam splitter, power recycling mirrors, and signal recycling mirrors. The system uses homodyne detection for improved quantum noise reduction. The interferometer's noise floor is determined by quantum, thermal, and technical noise. The design includes a 4-stage pendulum suspension for test masses, providing passive isolation and low thermal noise. The seismic isolation system uses multiple stages to minimize ground motion. The thermal compensation system addresses absorption in test mass coatings, reducing thermal lensing and surface distortion. The system includes active compensation for thermal aberrations in recycling cavities. The design aims to achieve a strain sensitivity of 10^-22 at 100 Hz, with a BNS detection range of 190 Mpc. The interferometer is expected to detect gravitational waves from compact binary coalescences and other astrophysical sources.The Advanced LIGO gravitational wave detectors are second-generation instruments designed for the two LIGO observatories in Hanford, WA and Livingston, LA. They are identical Michelson interferometers with 4 km long arms, featuring Fabry-Perot cavities and power recycling to enhance sensitivity. Advanced LIGO improves strain sensitivity by a factor of 10 over initial LIGO, extending the low-frequency sensitivity to 10 Hz. It uses signal recycling to improve frequency response and includes better seismic isolation and test mass suspensions. Data collection began in mid-2015. Advanced LIGO replaces all interferometer components with improved technologies, including larger test masses and better mirror coatings. A third interferometer is planned for India. The detectors are expected to detect dozens of compact binary coalescence sources per year. The interferometer uses a multi-stage Nd:YAG laser with up to 180 W output. The optical configuration includes a 50/50 beam splitter, power recycling mirrors, and signal recycling mirrors. The system uses homodyne detection for improved quantum noise reduction. The interferometer's noise floor is determined by quantum, thermal, and technical noise. The design includes a 4-stage pendulum suspension for test masses, providing passive isolation and low thermal noise. The seismic isolation system uses multiple stages to minimize ground motion. The thermal compensation system addresses absorption in test mass coatings, reducing thermal lensing and surface distortion. The system includes active compensation for thermal aberrations in recycling cavities. The design aims to achieve a strain sensitivity of 10^-22 at 100 Hz, with a BNS detection range of 190 Mpc. The interferometer is expected to detect gravitational waves from compact binary coalescences and other astrophysical sources.