An elementary proof by contradiction of the Collatz Conjecture (CC) (also known as the '3X+1' Conjecture), is presented. A modified form of the Collatz transformation is formulated, leading to the concept of a modified Collatz chain. A smallest counterexample N-0 is hypothesized; the existence of N-0 implies that N-0 must generate an infinite sequence {N-k}, each of whose elements is at least as large as N-0. A formula for Nk is derived, in terms of an auxiliary sequence {E-k} and the starting value N-0. It is shown that each Ek satisfies k <= E-k < 1.585k; this, in turn, leads us to conclude that N-0 is unbounded, which is a contradiction of its definition, thereby establishing CC.