Corals and tiny algae act as a team of engineers to form the building blocks needed to create the amazing coral reef ecosystem, which supports much of the marine life in the tropical oceans. These incredible ecosystems can extend for thousands of kilometers, like the Great Barrier Reef of Australia. Coral reefs would not exist without the help of the microscopic algae that associate with the coral and provide it with important nutrients for its survival. This article features the collaboration of amazing corals and their microalgae partners. You will learn about the processes that support the construction of coral reefs, their abilities to resist the threats that currently affect them (climate change, contamination), and the actions that can be taken to keep them safe and maintain the services that these ecosystems provide to other marine life.