Optical magnetometry uses resonant light interactions with atomic vapors to measure magnetic fields with high sensitivity. Recent advancements have improved traditional magnetometers for applications like geomagnetic anomalies and space measurements, and opened new areas such as bio-magnetic field detection, NMR, MRI, and inertial rotation sensing. Atomic magnetometers, which measure magnetic fields directly without cryogenic cooling, offer advantages over SQUID-based systems, achieving sensitivities rivaling or surpassing those of SQUIDs. The most sensitive is the spin-exchange-relaxation-free (SERF) magnetometer, with sensitivities below 10^-17 T/√Hz. These devices can achieve millimeter-scale spatial resolution and are used in diverse applications, including fundamental symmetry tests, biological magnetic field detection, and space missions. Atomic magnetometers operate by detecting changes in light polarization or intensity caused by magnetic field-induced spin precession in atoms. They can be configured to measure magnetic fields directly using fundamental constants, eliminating the need for calibration. The sensitivity is limited by quantum projection noise and photon shot noise, which can be reduced through techniques like spin squeezing and optimized optical pumping. Surface coatings and buffer gases help reduce spin relaxation, while increasing alkali-metal atom density enhances sensitivity. However, spin relaxation due to collisions between atoms limits sensitivity improvements. Atomic magnetometers are also used in fundamental physics, such as testing symmetries like parity and time-reversal invariance, and in nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) detection. They are particularly useful for detecting weak magnetic fields in space, where they can measure planetary and interplanetary magnetic fields with high precision. Cold atom magnetometry, using laser-cooled and trapped atoms, enables high-resolution magnetic imaging, useful for studying magnetic domains and currents in integrated circuits. Future developments in atomic magnetometry include robust laser-pumped devices, micro-fabricated magnetometers, and enhanced sensitivity for weak signals in various applications. Atomic magnetometers are expected to surpass SQUID sensors in sensitivity, enabling new discoveries in materials science and fundamental physics. The future of magnetic field measurement with atoms and light is promising, with continued advancements in technology and applications.Optical magnetometry uses resonant light interactions with atomic vapors to measure magnetic fields with high sensitivity. Recent advancements have improved traditional magnetometers for applications like geomagnetic anomalies and space measurements, and opened new areas such as bio-magnetic field detection, NMR, MRI, and inertial rotation sensing. Atomic magnetometers, which measure magnetic fields directly without cryogenic cooling, offer advantages over SQUID-based systems, achieving sensitivities rivaling or surpassing those of SQUIDs. The most sensitive is the spin-exchange-relaxation-free (SERF) magnetometer, with sensitivities below 10^-17 T/√Hz. These devices can achieve millimeter-scale spatial resolution and are used in diverse applications, including fundamental symmetry tests, biological magnetic field detection, and space missions. Atomic magnetometers operate by detecting changes in light polarization or intensity caused by magnetic field-induced spin precession in atoms. They can be configured to measure magnetic fields directly using fundamental constants, eliminating the need for calibration. The sensitivity is limited by quantum projection noise and photon shot noise, which can be reduced through techniques like spin squeezing and optimized optical pumping. Surface coatings and buffer gases help reduce spin relaxation, while increasing alkali-metal atom density enhances sensitivity. However, spin relaxation due to collisions between atoms limits sensitivity improvements. Atomic magnetometers are also used in fundamental physics, such as testing symmetries like parity and time-reversal invariance, and in nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) detection. They are particularly useful for detecting weak magnetic fields in space, where they can measure planetary and interplanetary magnetic fields with high precision. Cold atom magnetometry, using laser-cooled and trapped atoms, enables high-resolution magnetic imaging, useful for studying magnetic domains and currents in integrated circuits. Future developments in atomic magnetometry include robust laser-pumped devices, micro-fabricated magnetometers, and enhanced sensitivity for weak signals in various applications. Atomic magnetometers are expected to surpass SQUID sensors in sensitivity, enabling new discoveries in materials science and fundamental physics. The future of magnetic field measurement with atoms and light is promising, with continued advancements in technology and applications.