Quantum entanglement represents one of the most profound and counterintuitive phenomena in modern physics, fundamentally challenging classical notions of locality, causality, and separability. This comprehensive review examines the theoretical foundations of quantum entanglement, tracing its conceptual development from Einstein's critique of quantum mechanics through Bell's theorem to contemporary experimental verification. The paper synthesizes current understanding of entanglement's mathematical formalism, its role in violating Bell inequalities, and the resolution of the EPR paradox. Extensive discussion is devoted to landmark experiments that have conclusively demonstrated non-local correlations, including photon polarization studies, satellite-based quantum communication, and loophole-free Bell tests. The work further explores emerging technological applications in quantum cryptography, quantum computing, and quantum teleportation, while addressing fundamental questions regarding the nature of reality, information, and the relationship between quantum mechanics and general relativity. Finally, the paper examines open questions and speculative frameworks suggesting that entanglement may represent a foundational principle underlying spacetime geometry itself. Video documentation of this analysis is available at: https://www.youtube.com/watch?v=YDGKuXYRPpI.