A+ is a high-level, interactive, interpreted array programming language designed for numerically intensive applications, especially those found in financial applications.

In 1988, Arthur Whitney began work on the A programming language to replace APL. Other developers at Morgan Stanley extended it to A+, adding a graphical user interface (GUI) and other language features.

Arthur Whitney went on to create a proprietary array language named K. Like J, K omits the APL character set. It lacks some of the perceived complexities of A+, such as the existence of statements and two different modes of syntax.

A+ provides an extended set of functions and operators, a graphical user interface with automatic synchronizing of widgets and variables, asynchronous executing of functions associated with variables and events, dynamic loading of user compiled subroutines, and other features. A+ runs on many Unix variants, including Linux. It is free and open source software released under a GNU General Public License. A newer GUI has not yet been ported to all supported platforms.

The A+ language implements the following changes to the APL language:

Interactive A+ development is primarily done in the Xemacs editor, through extensions to the editor. Because A+ code uses the original APL symbols, displaying A+ requires a font with those special characters; a font named kapl is provided on the web site for that purpose.