Diplodocidae was named by Marsh (1884).

It was synonymized subjectively with Amphicoeliidae by Kuhn (1966); it was synonymized subjectively with Atlantosauridae by Bonaparte (1978); it was reranked as the unranked clade Diplodocidae by Tschopp et al. (2015), Mannion et al. (2019).

It was assigned to Sauropoda by Vetter (1884); to Opisthocoelia by Hay (1902); to Diplodocia by Tornier (1913); to Allophagi by Jaekel (1914); to Homalosauropodidae by Huene (1948), Young (1958); to Saurischia by Madsen and Miller (1979); to Sauropoda by Bakker (1986); to Neosauropoda by Wilson and Sereno (1994), Salgado et al. (1997); to Sauropoda by Jaekel (1911), McIntosh (1997); to Sauropoda by Marsh (1884), Marsh (1884), Marsh (1885), Marsh (1895), Marsh (1896), Marsh (1898), Huene (1908), Huene (1908), Huene (1909), von Zittel (1911), Huene (1914), Nopcsa (1923), Huene (1927), Huene (1927), Huene (1959), Galton (1977), Russell (1984), Bonaparte (1986), Carroll (1988), McIntosh (1990), Benton (1990), Bonaparte (1999); to Diplodocimorpha by Calvo and Salgado (1995), Salgado (1999); to Sauropoda by Dollo (1884), Dollo (1889), Zittel (1890), Winkler (1893), Nopcsa (1901), Mansel-Pleydell (1902), Joubert (1908), Arldt (1909), Matthew (1915), Lull (1924), Nopcsa (1928), Hay (1930), Roxo (1937), Kuhn (1946), Lapparent (1947), Bonaparte (1980), McIntosh (1981), Chure et al. (2006); to Diplodocoidea by Upchurch (1995), Upchurch (1995), Hunt et al. (1995), Wilson and Smith (1996), Sereno (1997), Upchurch (1997), Dong (1998), Sereno (1998), Wilson and Sereno (1998), Sereno (1999), Sereno et al. (1999), Wilson (2002), Upchurch et al. (2004), Apesteguía (2005), Remes (2006), Royo-Torres et al. (2007), Suteethorn et al. (2010), Wilson and Allain (2015); and to Flagellicaudata by Gallina and Apesteguía (2005), Taylor and Naish (2005), Rauhut et al. (2005), Salgado et al. (2006), Remes (2007), Remes (2009), Whitlock (2011), Ibiricu et al. (2012), Tschopp and Mateus (2013), Gallina et al. (2014), Tschopp et al. (2015), Mannion et al. (2019).