This lecture covers the principles of Quantum Metrology with Atoms in a Cavity, including spin-squeezing, many-body entangled states, and interaction-based quantum metrology. It explores the use of atomic sensors, such as atomic clocks and magnetometers, and the detection schemes involved. The presentation delves into the Jaynes-Cummings to Tavis-Cummings transition and the adiabatic elimination process. The lecture also discusses the design considerations for atomic sensors, the concept of squeezing, and the demonstration of squeezed states in atomic sensors. The instructor provides insights into the challenges of noise refocusing, Bell correlations, and the derivation of entanglement depth in quantum systems.