Lange's Theorem is a result in the field of complex analysis, specifically concerning the behavior of holomorphic functions. It states that if a function is holomorphic on a domain and has a certain type of growth condition, then it can be represented as a power series. This theorem helps in understanding how complex functions can be approximated and analyzed. The theorem is particularly useful in the study of analytic functions and their properties. It provides a framework for determining the convergence of power series and the conditions under which these series accurately represent holomorphic functions in a given region.