Uranium enrichment refers to a process to alter the isotopic composition of uranium. This is to produce fuel for nuclear power reactors, which requires a ²³⁵U content of about 3–5%, and to produce material for a nuclear weapon, which requires a ²³⁵U concentration of about 93%. A process that enriches reactor fuel can also enrich weapons material, which makes uranium enrichment a dual-use process. The line between civil and military purposes is very thin, and ways to broaden the line are being investigated. In this chapter, the fundamentals of uranium enrichment for these two purposes are discussed, the current Iranian nuclear situation assessed, and possible ways forward suggested for countries wanting to develop peaceful nuclear energy.