Sure, the STL has iterators, algorithms, and function objects, but for most C++ programmers, it s the containers that stand out. More powerful and flexible than arrays, they grow (and often shrink) dynamically, manage their own memory, keep track of how many objects they hold, bound the algorithmic complexity of the operations they support, and much, much more. Their popularity is easy to understand. They re simply better than their competition, regardless of whether that competition comes from containers in other libraries or is a container type you d write yourself. STL containers aren t just good. They re really good.