Many developmental biologists are interested in the molecular signals and cellular interactions that induce a group of cells to develop into a particular tissue. To investigate this, scientists can use a classic technique known as transplantation, which involves tissue from a donor embryo being excised and grafted into a host embryo. By observing how transplanted tissues develop in host environments, scientists have started to dissect the molecular pathways underlying development. In this video, we first look at the role of cellular interactions in development, and move on to a basic transplantation protocol. Finally, some specific developmental studies utilizing this technique are discussed, which examine the effect of tissue transplantation on the fate of donor and host tissue.