Ludwig Lejzer Zamenhof (1859-1917) was not the only one promoting the idea of a constructed language in his time. Numerous efforts - drawing inspiration from different sources - have shown a strong desire during the late 19th and early 20th century to create a mode of communication carried by universal humanitarianism. Esperanto, however, is unique in its influence. The articles collected in this volume debate the question of the extent to which this unique potential can be attributed to Jewish, cosmopolitan and pacifist traditions of thought. All contributions have resulted from the lectures of the international workshop "The heritage and legacy of Ludwik Lejzer Zamenhof between Judaism and Esperanto", that took place in the Museum Polin -