Across both vertebrates and invertebrates, epithelial tissues fulfill a wide variety of necessary functions. These tissues frequently line the interior of organs involved in the exchange of matter, such as the lung or the intestine, but can also be responsible for secreting hormones or digestive agents as is the case with the pancreas. Because they are responsible for transporting fluids, many epithelial tissues contain an internal lumen and can have incredibly complex and branched architectures while still maintaining a continuous sheet. The epithelial tubes that comprise a single organ do not always develop together in the embryo; as such, mechanisms are needed to bring together and fuse distinct epithelial structures. These processes are observed notably in the Drosophila tracheal system, in the mammalian pancreas, and in the avian lung. Although the physical steps of epithelial fusion have been well described for select systems, the underlying molecular mechanisms remain unclear. This continues to be an active area of research with an abundance of potential health applications related to understanding developmental anomalies in these organs. By comparing how different organisms accomplish epithelial fusion, we hope to expand the engineering toolbox with which these anomalies can be treated.