In a doubly linked list, there are two links on each node: one to point to the next node and another one to the previous node. Where the singly linked list is unidirectional, the doubly linked list is bidirectional. We can move forward or backward in the list without any problem. The following image shows a sample doubly linked list. Later, in the Implementing a doubly linked list in PHP section, we will explore how to implement a doubly linked list: