The human brain is endlessly fascinating and mysterious, but the majority of brain research to date has focused on neurons and their functions. While the other types of brain cells, such as astrocytes and glia, are starting to get their due, there is another element of the brain that to this day has gone woefully unstudied: the cerebrospinal fluid (CSF) and the brain structure that produces it, the choroid plexus. The CSF is a clear, colorless fluid found in the brain and spinal cord, and is traditionally thought to protect the brain from injury by acting as a shock absorber. In this episode, Madeline Lancaster, a Group Leader at the MRC Laboratory of Molecular Biology in Cambridge and Lauren Richardson discuss the article "Human CNS barrier-forming organoids with cerebrospinal fluid production" by Laura Pellegrini, Claudia Bonfio, Jessica Chadwick, Farida Begum, Mark Skehel, Madeline A. Lancaster published in Science. The paper describes a new model for studying the CSF and the choroid plexus by creating what’s sometimes called a mini-brain or a brain-in-a-dish, but is more accurately known as a cerebral organoid. With this model, Dr. Lancaster and her team were able to reveal new insights into the composition and function of the choroid plexus, and importantly, how it forms a key barrier between the blood and the brain. We discuss the how these organoids can be used to study brain development, evolution, and improve the drug development process.