Human health is undeniably a topic of intense research focus today. It's an issue that affects each one of us personally–including our friends, family, and colleagues–while also having a global impact. We are constantly bombarded by environmental insults that can affect our health, from the relatively innocuous irritants that cause allergies to potentially deadly viruses, parasites, and bacteria. Our most effective defense against these microscopic invaders is our immune system. One institution that has focused on unraveling some of the remaining questions in immunology is the RIKEN Research Center for Allergy and Immunology (RCAI). In this booklet, we invite you to read a sampling of RCAI publications that have shed light on topics such as immune cell development and differentiation, the protective role of probiotics, immune system homeostasis, and the role of immune cells in cancer and autoimmune diseases.