Abstract: Colloidal quantum dots (CQDs), with size-tunable bandgaps, excellent optoelectronic properties, and solution processability, hold great promise for optoelectronic applications. Nevertheless, conventional synthesis methods are limited by complex procedures, lattice defects, and poor monodispersity. Cation exchange has emerged as an efficient and versatile strategy for the controlled preparation of CQDs. Firstly, this review outlines its mechanisms and applications, emphasizing the critical conditions for maintaining the original size and morphology of quantum dots: When the CQDs size exceeds a threshold or the synthesis temperature is below a critical value, their size and morphology are maintained; otherwise, dissolution and recrystallization occur, altering the reaction mechanism. Next, recent progress in complete cation exchange for single-component CQDs and partial exchange for heterostructured nanocrystals has been summarized, highlighting their unique properties in this review. A comparative analysis further shows that cation exchange enables superior device performance compared with hot-injection methods. Finally, future directions about cation exchange in material development, green synthesis, and multifunctional optoelectronic devices are discussed, offering fresh insights for advancing CQDs' research and applications.