  2019 marked the 75th anniversary of the publication of Erwin
Schr\"{o}dinger's "What is Life?", a short book described by Roger Penrose in
his preface to a reprint of this classic as "among the most influential
scientific writings of the 20th century." In this article, I review the long
argument made by Schr\"{o}dinger as he mused on how the laws of physics could
help us understand "the events in space and time which take place within the
spatial boundary of a living organism." Though Schr\"{o}dinger's book is often
hailed for its influence on some of the titans who founded molecular biology,
this article takes a different tack. Instead of exploring the way the book
touched biologists such as James Watson and Francis Crick, as well as its
critical reception by others such as Linus Pauling and Max Perutz, I argue that
Schr\"{o}dinger's classic is a timeless manifesto, rather than a dated
historical curiosity. "What is Life?" is full of timely outlooks and approaches
to understanding the mysterious living world that includes and surrounds us and
can instead be viewed as a call to arms to tackle the great unanswered
challenges in the study of living matter that remain for 21$^{st}$ century
science.
