<p>The capability to modify the crystal phase of semiconductor materials at the nanoscale marks a major milestone in modern materials engineering. While early research focused on developing epitaxial methods for deterministic crystal phase control, recent advances have highlighted the emergence of novel device functionalities unlocked by phase-engineered semiconductor nanostructures. Here, we provide a comprehensive overview of the field, beginning with a summary of the progress in crystal phase engineering through direct nanostructure epitaxy. We then move on to discuss advances in the crystal structure transfer method, a promising technique for broadening the material scope of crystal phase engineering. Finally, we identify key challenges and outline future pathways toward realizing next-generation devices built on phase-engineered semiconductor platforms.</p> Graphical abstract <p></p>