Abstract : An interlacing theorem in Matrix Theory known as Cauchy's interlacing theorem gives interlacing properties of the eigenvalues of a Hermitian matrix A and a larger bordered Hermitian matrix. The standard proof Cauchy's interlacing theorem usually follows from the Courant-Fischer theorem. I will present a proof of Cauchy's interlacing theorem using elementary ideas. Some easy consequences as well as a converse will be indicated, time permitting.