IDEA is the cornerstone federal law that safeguards and promotes the educational rights of children with disabilities. It was enacted in 1975 as the Education for All Handicapped Children Act (EHA), which established a right to a free appropriate public education (FAPE) for all children with disabilities for the first time. Before the EHA, there were gradual changes in laws regarding the treatment and support of individuals with disabilities, driven by legal actions and advocacy from disability rights groups. Over time, these efforts led to the more comprehensive approach seen in the EHA. Since its inception, IDEA has been reauthorized four times, including in 1990 when it acquired its current name. IDEA influences state and local funding decisions both by tying eligibility for IDEA grants -- which represent a substantial share of total funding for special education from all sources -- to meeting specific programmatic and administrative requirements and by requiring states and public school systems to sustain at least the same levels of state and local funding for special education year over year. This brief provides an overview of the purposes of IDEA and the four categories of federally funded programs governed by the law.