The Stanford Research Institute Problem Solver, known by its acronym STRIPS, is an automated planner developed by Richard Fikes and Nils Nilsson in 1971 at SRI International. The same name was later used to refer to the formal language of the inputs to this planner. This language is the base for most of the languages for expressing automated planning problem instances in use today; such languages are commonly known as action languages. This article only describes the language, not the planner.

A STRIPS instance is composed of:

Mathematically, a STRIPS instance is a quadruple ${\displaystyle \langle P,O,I,G\rangle }$, in which each component has the following meaning:

A plan for such a planning instance is a sequence of operators that can be executed from the initial state and that leads to a goal state.

Formally, a state is a set of conditions: a state is represented by the set of conditions that are true in it. Transitions between states are modeled by a transition function, which is a function mapping states into new states that result from the execution of actions. Since states are represented by sets of conditions, the transition function relative to the STRIPS instance ${\displaystyle \langle P,O,I,G\rangle }$ is a function

where ${\displaystyle 2^{P}}$ is the set of all subsets of ${\displaystyle P}$, and is therefore the set of all possible states.

The transition function ${\displaystyle \operatorname {succ} }$ for a state ${\displaystyle C\subseteq P}$, can be defined as follows, using the simplifying assumption that actions can always be executed but have no effect if their preconditions are not met:

The function ${\displaystyle \operatorname {succ} }$ can be extended to sequences of actions by the following recursive equations: