Function descriptions pervade human daily life and various scientific domains. Functions play an instrumental role in many scientific explanations. They are commonly used to explain the existence and performance of biological traits, as well as in design and malfunction explanations in engineering science. Additionally, they are essential in social science. However, the ubiquity of function as a concept makes it difficult to fully grasp its meaning. In the philosophy of science, there is no consensus on how to define function in general, nor is there a unified account of functional explanations across scientific fields such as the life sciences, engineering sciences, and social sciences. This project takes up this challenge by approaching the problem in an innovative way. Rather than attempting to construct a unified theory of function head-on—a task widely considered nearly impossible—it first investigates the general properties of function from a pluralist stance. By identifying the key differences and essential attributes of functional explanations across scientific domains, it provides an overarching framework to integrate functional explanations in these three fields. The result of a successful integration will ultimately lead to an epistemology of explanatory integration, contributing to discussions on scientific explanation both in theory and in practice.