Abstract: I will review and discuss in detail type II string theory on $AdS_3\times S^3\times T^4$ and its $1+1$ dimensional superconformal field theory dual, emphasizing the string theoretic aspects of this duality. For one unit of NS-NS 5-brane flux ($Q_5=1$), this string theory has been suggested to be dual to a grand-canonical ensemble of $T^{4N}/S_N$ free symmetric orbifold CFTs, and one goal will be to understand how this is consistent and how it fits with the description of other values of $Q_5$. I will discuss how the strong coupling limit of the NS-NS string theory arises (even at large $N$) in the free orbifold description, and why this limit does not have a weakly coupled R-R description. The dual CFT includes (for all values of $Q_5$) an extra $T^4$ factor that is decoupled from perturbative string theory, and I will discuss how this appears and how it is coupled to the CFT.