In this unit, we have learned how the stacks are implemented using arrays and using liked list. Also, the advantages and disadvantages of using these two schemes were discussed. For example, when a stack is implemented using arrays, it suffers from the basic limitations of an array (fixed memory). To defeat this problem, stacks are implemented through linked lists. This unit also introduced learners to the concepts of multiple stacks. The problems related with the implementation of multiple stacks are also covered.