Inclusion Criteria:  Parent/caregiver must be willing and able to provide written informed consent electronically prior to entering data into the registry. Rett individuals of any age, living or deceased, must have a diagnosis of Rett syndrome and/or have a mutation in MECP2.  Exclusion Criteria:  Individuals who have a genetic mutation that is inconsistent with Rett syndrome or who have a different disorder. Individuals with MECP2 Duplication Syndrome