Gold nanoparticles possess a unique combination of properties which allow them to act as highly multifunctional anti-cancer agents (X. H. Huang, P. K. Jain, I. H. El-Sayed and M. A. El-Sayed, Nanomedicine, 2007, 2, 681-693; P. Ghosh, G. Han, M. De, C. K. Kim and V. M. Rotello, Adv. Drug Delivery Rev., 2008, 60, 1307-1315; S. Lal, S. E. Clare and N. J. Halas, Acc. Chem. Res., 2008, 41, 1842-1851; D. A. Giljohann, D. S. Seferos, W. L. Daniel, M. D. Massich, P. C. Patel and C. A. Mirkin, Angew. Chem., Int. Ed., 2010, 49, 3280-3294). Not only can they be used as targeted contrast agents for photothermal cancer therapy, they can serve as scaffolds for increasingly potent cancer drug delivery, as transfection agents for selective gene therapy, and as intrinsic antineoplastic agents. This tutorial review will highlight some of the many forms and recent applications of these gold nanoparticle conjugates by our lab and others, as well as their rational design and physiologic interactions.