Universally translated into English as “mode,” the Russian term лад (“lād”) first appeared in 1830 as a translation from German Tonart, which is usually translated into English as “tonality.” To Tchaikovsky a lād was, in fact, a tonality, but by century’s end lād had come to signify its pre-tonal cousin, mode. Boleslav Yavorsky’s work on the subject in the early twentieth century gave lād new post-modal and post-tonal meaning with respect to quasi-tonal and post-tonal music. In this article, I delve deeply into the history of this uniquely Russian concept, from its inception to its highly modified mid-twentieth century form. Rather than trying to find an English equivalent, I leave “lād” in its transliterated form, which disentangles it from inaccurate translations. I examine a 1945 Chopin analysis by Yavorsky’s student, Sergei Protopopov, which outlines new interpretations for Russian lād. Sketches for this analysis, from the Russian National Museum of Music, provide a backdrop for a reexamination of basic tonal constructs such as cadence, phrase, form, harmonic function, and melodic diminution. I then look at a famous 1930 conference on Yavorsky’s theories as an example of the high stakes involved in creating a Marxist musical science, in which lād played a primary role. I also briefly discuss Yavorsky’s theories as a counterweight to Hugo Riemann’s encroaching functionality, which was brought to Russia by Gregori Catoire in the early twentieth century. It is my hope that this work on lād will fill in many gaps for the English-language reader, and possibly spur further studies on this uniquely Russian concept.