The objective of this chapter is to present a broad discussion on reproductive and obstetrical infectious diseases. Infectious diseases occurring in pregnancy can pose a threat to the fetus and are the major cause of bad obstetric history. Most maternal infections are asymptomatic, necessitating both a high degree of clinical awareness and adequate early screening. In pregnant women, group B streptococcus (GBS) is a cause of cystitis, amnionitis, endometritis and stillbirth. Occasionally, GBS may cause bacteremia leading to meningitis and endocarditis in pregnant women, while in postpartum women, GBS has been identified as a cause of UTIs and pelvic abscesses. The definitive diagnosis of invasive GBS infection is the isolation of the organism from a normally sterile body site such as blood or CSF. Listeriosis, lessons for the clinician, syphilis, gonococcal infections, Trichomonas vaginalis, bacterial vaginosis, vulvovaginal candidiasis, pelvic inflammatory diseases, congenital infections, shell vial assay, maternal cytomegalovirus infection, hepatitis B virus and hepatitis C virus, etc. are various other important reproductive and obstetrical infectious diseases which are discussed throughout this chapter.