Newton's method is an iterative method used to find successively better approximations to the roots, or zeroes, of a real-valued function. It works by taking an initial guess, calculating the tangent line to the function at that point, and using the x-intercept of the tangent line as the next guess. The process is repeated by calculating new tangent lines until an accurate value is reached. Newton's method can also be extended to complex functions and systems of equations.