I will start by discussing the 4d N=4 supersymmetric Yang-Mills theory on two spaces with a boundary - a half-line (times three infinite dimensions) and four dimensional anti-de Sitter space. I will review in detail the possible choices of boundary conditions for this theory, and then exhibit the solutions of string theory (supergravity) that are holographically dual to the N=4 SYM theory on these spaces. The same methods used to obtain these duals can also be used to find duals for 3d N=4 and 4d N=2 superconformal field theories that appear in brane configurations, and I will discuss these solutions as well.