JARDIN wants to serve as a bridge for access to information about European Reference Networks, to make them more visible and to raise awareness of their work. We have compiled a list of reference websites with relevant information on rare diseases, undiagnosed diseases and complex conditions, as well as on the ERNs and all that implies their role in the health and care pathway. We intend to make JARDIN a place where the most important sites on rare diseases or complex conditions can be accessed, in order to facilitate access to information, tools and resources for healthcare professionals, patients, patient associations, researchers and all members of the public interested in this important area of health. We invite you to explore the resources and discover documentation, guides, training materials and other useful tools for everyone. Because rare diseases and complex conditions, such as undiagnosed diseases, affect us all as a society, and we need to be aware of them. We will be updating this list to keep you informed of the latest online resources.