Self-assembled porphyrin and macrocycle derivatives. Porphyrins are catalyst molecules in natural systems; for example, chlorophyll in leaves that activates the reaction for capturing CO2, converting sunshine energy into chemical energy, and storing the energy. The articles in this issue cover the synthesis and formation mechanisms of artificial porphyrin-based nanostructures by self-assembly methods and their applications in solar-energy harvesting, water splitting, environmental pollutant reduction, and nanomedicine for tumor therapy. The cover shows the molecular structure of a porphyrin. The inserts around the molecular structure are electron microscope images of the nanostructures of selfassembled porphyrins that enable highly efficient photocatalytic processes.See the technical theme that begins on page 167.