ALT Molecular cages: emerging applications in diverse fields Molecular cages are specially designed supramolecular structures with tiny cavities that can hold specific guest molecules. Because of this, they have many useful applications, including detecting substances, speeding up chemical reactions, and environmental cleanup. In their Review, Martí-Centelles and colleagues showcase recent research that has shown that by adjusting the cage design—using either organic materials or metal-organic frameworks—scientists can create cages with tailored functions. These advances allow molecular cages to be used in a diverse range of innovative ways, from simple molecule trapping to mimicking complex biological systems. Cover artwork credit: Vicente Martí-Centelles.