Placental inflammatory lesions are important findings that lead fetal and neonatal morbidity and mortality, and can be divided into two broad subcategories, acute inflammation caused by microorganisms and chronic inflammation caused by host immune responses. Recently, a diagnostic framework for these lesions has been established, and uniform diagnostic criteria have been recommended by the Amsterdam International Consensus Group. Chorioamnionitis is representative of the acute inflammatory lesion, and is the most frequent pathological diagnosis in placental pathology. The hallmark of chorioamnionitis is neutrophil infiltration in the membrane/chorioamnionic plate and fetal vessels. The inflammatory response can be both maternal (inflammation in the membrane or chorioamnionic plate) and fetal (inflammation in the fetal vessels—umbilical vessels or chorionic vessel). Recent studies have shown that the fetal inflammatory response is associated with neonatal mortality and morbidity. Furthermore, chronic inflammatory lesions, such as villitis of unknown etiology and chronic histiocytic intervillositis, are also important. Although their etiology remains unknown, the maternal immune response against paternal antigens has been considered a possible factor. These inflammatory lesions are associated with fetal demise and fetal growth restriction. Inflammatory lesions in the placenta are useful for understanding intrauterine conditions, guiding treatment, and predicting complications.