The Spectral Theorem is a fundamental result in linear algebra that applies to self-adjoint or normal operators on Hilbert spaces. It states that such operators can be represented in terms of their eigenvalues and eigenvectors, allowing them to be diagonalized. This means that any self-adjoint operator can be expressed as a sum of projections onto its eigenvectors, weighted by their corresponding eigenvalues. This theorem is crucial in various fields, including quantum mechanics, where it helps in understanding observable quantities. By providing a clear structure to operators, the Spectral Theorem simplifies many problems in mathematics and physics, making it easier to analyze complex systems.