Chorioamnionitis refers to inflammation of the chorioamniotic membranes. Five related terms are (1) clinical chorioamnionitis, a syndrome characterized by maternal and fetal signs of inflammation (e.g. maternal fever, fetal tachycardia); (2) histologic acute chorioamnionitis, the presence of inflammation in the chorioamniotic membranes or the chorionic plate of the placenta; and (3) intra-amniotic inflammation refers to the presence of an inflammatory process in the amniotic fluid (e.g. elevated white blood cell count or inflammatory markers such as interleukin-6). Intra-amniotic inflammation may be due to (4) intra-amniotic infection when bacteria are present or (5) sterile intra-amniotic inflammation in the absence of microorganisms. Each of these terms refers to a different condition and should not be used synonymously. Clinical chorioamnionitis is the most common infection-related diagnosis affecting 1–6% of all gestations. It is an antecedent to puerperal infections such as endometritis, pelvic peritonitis, and pelvic abscesses with an increased risk of uterine atony, postpartum haemorrhage, wound infections, and necrotizing fasciitis as well as neonatal sepsis.