This cover was designed by Dr. Yu Zhang (Ph.D. 2013) for an invited essay (Are We Entering the Nano Era? by Y. Xia, pp. 12268-12771) and an invited review article (Engineered Nanoparticles for Drug Delivery in Cancer Therapy by T. Sun, Y. S. Zhang, B. Pang, D. C. Hyun, M. Yang and Y. Xia, pp.12320-12364) published in Angewandte Chemie International Edition (2014, vol. 53), a special issue on nanotechnology, nanomaterials, nanotoxicology and nanomedicine. It shows that nanomaterials is a double-side sword: although the potential of nanotechnology is tremendous, questions remain about the long-term safety of nanomaterials and the risk-benefit characteristics of their usage.