The objective of this chapter is to introduce the intrauterine insemination. An IUI stands for intrauterine insemination. It is a commonly used treatment for infertility. In IUI, washed semen from husband or donor is artificially inseminated into the uterus of female partner. This chapter discusses the indications, contraindications, the procedure, and success rate with IUI. Indications of IUI include unexplained infertility, minimal and mild endometriosis, anovulatory infertility, mild male factor infertility, azoospermia (donor sperm insemination), and ejaculatory dysfunction. Contraindications of IUI include bilateral tubal blockage, ovarian failure, cervical atresia, severe male factor infertility, and advanced stages of endometriosis. List of possible mechanism of action of intrauterine insemination and planning of intrauterine insemination cycle are also discussed in this chapter.