Pietersma's Theorem is a result in the field of mathematics, specifically in the area of functional analysis. It provides conditions under which certain types of linear operators can be approximated by simpler operators. This theorem is particularly useful in the study of Banach spaces and Hilbert spaces, where understanding operator behavior is crucial. The theorem is named after the mathematician Henk Pietersma, who contributed to the understanding of operator theory. Pietersma's Theorem helps mathematicians analyze the stability and convergence of sequences of operators, making it a valuable tool in both theoretical and applied mathematics.