One of the greatest unsolved problems in physics is the unification of quantum mechanics and general relativity. Gravitation is described by general relativity, whereas quantum mechanics describes the behavior of matter at the microscopic level and other known interactions in nature, including electromagnetism. String theory has been used to bridge the gap between these two theories, since it provides a consistent theory of quantum gravity. In string theory, all fundamental particles are tiny strings vibrating in spacetime. A remarkable feature of string theory is holography, which states that when you have a string theory in a given volume, it can be completely reconstructed using only the information on the boundary of that volume. Holography occurs in gravitational theories, and as such, we will develop new techniques to understand it and quantum gravity by analytically calculating all the interactions of some string theories and filed theories on the boundary, such as N=4 Super-Yang-Mills.