There are four serotypes of dengue (DEN1-DEN4) virus that are endemic in most areas of Southeast Asia, Central and South America, and other subtropical regions. The number of cases of severe disease associated with DEN virus infection is growing because of the continued spread of the mosquito vector, Aedes aegypti, which transmits the virus to humans. Infection with DEN virus can result in an asymptomatic infection, a febrile illness called dengue fever (DF), and the very severe disease called dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Currently, a licensed vaccine is not available. However, a tetravalent vaccine is urgently needed to prevent DF and DHF/DSS, the latter of which occurs predominantly in partially immune individuals. A live attenuated, tetravalent DEN virus vaccine candidate has been generated using reverse genetics that is able to provide immunity to each of the four serotypes of DEN. Attenuation has been achieved by generating recombinant DEN (rDEN) viruses which are modified by deletion or, alternatively, by antigenic chimerization between two related DEN viruses using the following two strategies: 1) introduction of an attenuating 30 nucleotide deletion (Delta30) mutation into the 3' untranslated region of DEN1 and DEN4; and 2) replacement of structural proteins of the attenuated rDEN4Delta30 vaccine candidate with those from DEN2 or DEN3. Attenuation of the four monovalent vaccine candidates has been achieved for rhesus monkeys or humans and an immunogenic tetravalent vaccine candidate has been formulated. The level of attenuation of each dengue vaccine component can be increased, if needed, by introduction of additional attenuating mutations that have been well characterized.