The Lex Papia Poppaea was a Roman law introduced in 9 AD to encourage and strengthen marriage. It included provisions against adultery and celibacy and complemented and supplemented Augustus' Lex Julia de Maritandis Ordinibus of 18 BC and the Lex Iulia de Adulteriis Coercendis of 17 BC. The law was introduced by the suffect consuls of that year, Marcus Papius Mutilus and Quintus Poppaeus Secundus, although they themselves were unmarried.
Tacitus mentions several leges Iuliae (Julian Laws) pertaining to morals and marriage, and the Lex Papia Poppaea as a separate later law, refining the Julian Laws (Annals, 3.25)
Some writers conclude from the passage in Suetonius (Suet. Aug. 14) that the Lex Julia de Maritandis Ordinibus of 18/17 BC was rejected, and add that it was not enacted until 4 AD. In the year 9 AD, and in the consulship of Marcus Papius Mutilus and Quintus Poppaeus Secundus (consules suffecti), another law was passed as a kind of amendment and supplement to the former law, and hence arose the title of Lex Julia et Papia Poppaea by which these two laws are often quoted. It has been inferred from the two laws being separately cited that they were not made into one.
The 6th century Digest only mentions the Lex Julia de Maritandis Ordinibus (Dig. 38 tit.11; Dig. 23 tit.2).
Various titles are used according as reference is made to the various provisions; sometimes the reference is to the Lex Julia, sometimes Papia Poppaea, sometimes Lex Julia et Papia, sometimes Lex de Maritandis Ordinibus, from the chapter which treated of the marriages of the senators (Gaius, i.178; Ulp. Frag. xi.20; Lex Marita, Hor. Carm. Sec.), sometimes Lex Caducaria, Decimaria, etc. from the various chapters (Ulp. Frag. xxviii tit.7; Dion Cass. liv.16, lvi.1, &c.; Tacit. Ann. iii.25). (see References)