Nial (from "Nested Interactive Array Language") is a high-level array programming language developed from about 1981 by Mike Jenkins of Queen's University, Kingston, Ontario, Canada. Jenkins co-created the Jenkins–Traub algorithm.

Nial combines a functional programming notation for arrays based on an array theory developed by Trenchard More with structured programming concepts for numeric, character, and symbolic data.

It is most often used for prototyping and artificial intelligence.

In 1982, Jenkins formed a company (Nial Systems Ltd) to market the language and the Q'Nial implementation of Nial. As of 2014, the company website supports an Open Source project for the Q'Nial software with the binary and source available for download. Its license is derived from Artistic License 1.0, the only differences being the preamble, the definition of "Copyright Holder" (which is changed from "whoever is named in the copyright or copyrights for the package" to "NIAL Systems Limited"), and an instance of "whoever" (which is changed to "whomever").

Nial uses a generalized and expressive Array Theory in its Version 4, but sacrificed some of the generality of functional model, and modified the Array Theory in the Version 6. Only Version 6 is available now.

Nial defines all its data types as nested rectangular arrays. ints, booleans, chars etc. are considered as a solitary array or an array containing a single member. Arrays themselves can contain other arrays to form arbitrarily deep structures. Nial also provides Records. They are defined as non-homogenous array structure.

Functions in Nial are called Operations. From Nial manual: "An operation is a functional object that is given an argument array and returns a result array. The process of executing an operation by giving it an argument value is called an operation call or an operation application."

Nial like other APL-derived languages allows the unification of binary operators and operations. Thus the below notations have the same meaning. Note: sum is same as +