Originating from the work of De Morgan (150 years ago!), CSS Peirce and Schröder, and getting its present equational form from the contributions of Tarski in the 1940s, the calculus of binary relations remained a mathematical curiosity until some researchers started to draw connections with various areas of mathematics and computer science.

I will present the calculus, its chronology and short examples illustrating current application areas including ongoing research taking place in our group after the introduction of the subject by Jim Lipton.