Abstract: The storyline of a dynamically generated entertainment program, such as a video game, is generated using a matrix of reusable storyline fragments called substories. A set of characters that participate in the storyline is established and a set of reusable substories is defined. Each substory represents a "fragment of a story", usually involving an action by a subject, where the subject is one of the characters. Most substories can be reused multiple times with different ones of the characters being the subject and different ones of the characters being the direct object of the substory. Each substory has a set of possible reaction substories, which are a subset of the defined substories. A plan list stores plan data indicating ones of the substories to be performed at specified times. An initial "seed story" in the form of an initial set of substories is stored in the plan list. The substories stored in the plan list are executed at times corresponding to their respective specified times.