The Three Marks of Existence are fundamental concepts in Buddhism that describe the nature of all phenomena. They include impermanence (anicca), suffering (dukkha), and non-self (anatta), which together illustrate the transient and often painful nature of existence. Understanding these marks is essential for grasping the concept of rebirth, as they highlight the cycle of suffering and the importance of realizing the illusory nature of the self in breaking free from this cycle.