"Joy is a functional programming language which is not based on the application of functions to arguments but on the composition of functions. This paper compares and contrasts Joy with the theoretical basis of other functional formalisms and the programming languages based on them. One group comprises the lambda calculus and the programming languages Lisp, ML and Miranda. Another comprises combinatory logic and the language FP by Backus. A third comprises Cartesian closed categories. The paper concludes that Joy is significantly different from any of these formalisms and programming languages."