Cellular senescence is defined as a state of stable cell cycle exit in response to various stimuli, which includes both cytotoxic stress and physiological cues. In addition to the core non-proliferative aspect, senescence is associated with diverse functionalities, which contribute to the role of senescence in a wide range of pathological and physiological processes. Such functionality is often mediated by the capability of senescent cells to communicate with their surroundings. Emerging evidence suggests that senescence is not a single entity, but a dynamic and heterogeneous collective phenotype. Understanding the diverse nature of senescence should provide insights into the complexity of tissue homeostasis and its disruption, such as in aging and tumorigenesis.