In this talk I will introduce my research on black holes, string theory and holography. After a general motivation I will first discuss my work on higher-dimensional black holes, specifically what distinguish them from four-dimensional black holes, how to classify them and how to construct new types of solutions. I will then go on to introducing my work on the AdS/CFT correspondence. I explain my results on matching of the Hagedorn temperature of gauge theory and string theory in AdS/CFT and discuss the potential future applications of this. I will end with mentioning recent work on the new AdS_4/CFT_3 correspondence.