Slavic constructed languages have been widely neglected by interlinguistics and Slavic linguistics so far; however, the number of projects for a common Slavic language has been growing since the 17th century, beginning with Juraj Križanić’s Ruski jezik (1666) and continuing up to Arnošt Eman Žídek’s Slovan (1940) and beyond. The construction of Slavic languages has recently been experiencing a revival through the spread of the internet since the 1990s. This has manifested itself mainly in three extensively elaborated projects with their own websites and user communities: Slovio (1999), Slovianski (2006) and Novoslovienski (2010). These three projects — one of them schematic, two of them naturalistic — are presented in the historical context of Slavic language construction from the 17th century up to the present and analyzed structurally in terms of their writing systems, their grammars and the composition of their lexicons. Although their chances of implementation in practice in the context of European language policy are currently rather marginal, they should be valued as a unique phenomenon in Slavic cultural history.