Polyelectrolytes have found utility across various applications in materials science, from electrochemical devices to biotechnology, due to their facile processing and tunable properties. Through chemistry, rational manipulation of molecular structure enables individual families of polyelectrolytes to be used in emerging advanced applications. In this perspective, we focus on cationic systems, and we describe how various structural motifs influence macromolecular properties for anion exchange membranes and gene delivery vectors. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3167-3174