May 1, 2024
Updated June 28, 2025
16 minute read
An Introduction to Behavior Trees
Behavior Trees, often abbreviated as BTs, are a powerful tool used to create decision-making logic for autonomous agents. Think of a BT as a highly organized flowchart for actions and choices. It's a mathematical model that allows developers to construct complex behaviors from a collection of simple, modular tasks. This hierarchical structure enables the creation of sophisticated and reactive artificial intelligence (AI) that can adapt to changing environments. Their strength lies in this ability to build very complex tasks from simple ones without needing to worry about the low-level details of how each simple task is implemented.
The core purpose of a Behavior Tree is to provide a more intuitive and scalable way to design AI compared to other methods. They are especially popular in fields like video game development and robotics, where creating believable and intelligent characters or autonomous systems is crucial. In a video game, a BT might dictate how a non-player character (NPC) patrols an area, engages in combat, or flees from danger. In robotics, a BT could guide a robot through a complex assembly task, navigate an unknown space, or interact with objects. The visual and modular nature of BTs makes them easier to design, test, and debug, which is a significant advantage when dealing with the intricate logic that modern AI demands.
Core Concepts of Behavior Trees
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Reading list
We've selected 21 books
that we think will supplement your
learning. Use these to
develop background knowledge, enrich your coursework, and gain a
deeper understanding of the topics covered in
Behavior Trees.
This is considered the first comprehensive book on Behavior Trees and provides both a broad introduction and an in-depth exploration of the topic. It covers fundamental concepts like semantics and design principles, as well as advanced topics such as learning and task planning. is suitable for students and professionals and can serve as a primary textbook or a comprehensive reference.
This comprehensive guide covers the fundamentals of behavior trees, their design, implementation, and use in robotics and AI applications. It is suitable for practitioners and researchers seeking a thorough understanding of behavior trees.
This comprehensive survey paper provides a thorough overview of the state-of-the-art in behavior trees. Written by pioneers in the field of reinforcement learning, it offers valuable insights for researchers and practitioners.
Written by a pioneer in the field of AI, this book provides a comprehensive overview of behavior trees in the context of artificial intelligence. It covers both theoretical and practical aspects.
This third installment of the Game AI Pro series presents more recent perspectives and techniques in game AI, with likely inclusion of advanced topics or novel applications of Behavior Trees. It serves as a valuable resource for staying current on industry practices and exploring more complex uses of Behavior Trees in modern games. It is best suited as supplementary material and a reference for advanced topics.
This compilation of articles from industry professionals on various game AI topics. It includes contributions specifically on Behavior Trees, offering practical insights and real-world applications. While not a structured textbook, it's an invaluable resource for understanding contemporary practices and gaining different perspectives on implementing Behavior Trees in games. It's best used as supplementary reading and a reference for specific techniques.
Series compiles articles and chapters from experienced game AI professionals. It often includes discussions and case studies on the practical implementation and challenges of using Behavior Trees in commercial games. It's a valuable resource for gaining insights into real-world applications and advanced techniques.
This title suggests a focus specifically on the importance and role of Behavior Trees in contemporary game AI. It likely covers the fundamental concepts and explains why BTs have become a popular choice in the industry. This would be a good resource for a foundational understanding of BTs in games.
While not solely focused on Behavior Trees, this widely-used textbook for game AI includes significant coverage of the topic within the broader context of AI techniques used in games. It's an excellent resource for gaining a general understanding of how Behavior Trees fit into game AI development and provides practical examples. is valuable as a primary text for game AI and a strong reference for Behavior Trees in that domain.
Specifically focuses on implementing AI within the Unity game engine and includes dedicated content on Behavior Trees. It's highly practical for those working with Unity, providing concrete examples and guidance on integrating Behavior Trees into game projects. It serves as a practical guide and reference for Unity developers.
This resource highlights the application of Behavior Trees in a specific domain outside of traditional game AI, such as controlling Unmanned Aerial Vehicles (UAVs). It showcases the versatility of BTs and their applicability in robotics and control systems, providing examples of how BTs are used for mission management. Useful for understanding applications in robotics.
Provides a broad overview of various game AI techniques with practical C++ examples. While it may not have extensive dedicated coverage solely on Behavior Trees, it often includes them as one of the fundamental AI architectures. It's a good resource for understanding the implementation of AI in games at a foundational level and can provide context for Behavior Trees alongside other methods.
A resource focusing purely on the theory behind Behavior Trees would delve into their mathematical model, properties, and formal analysis. This is crucial for a deep understanding of why BTs work and their capabilities and limitations. This is best suited for those seeking a rigorous theoretical foundation.
Covers a range of AI techniques for games, and while the extent of Behavior Tree coverage may vary by edition, it provides a good overview of how different AI methods are synthesized and collaborate in game environments. It can help position Behavior Trees within a larger AI system architecture. Useful for gaining a broader perspective on game AI.
The AI Wisdom series (various volumes) often contains articles on specific AI techniques used in games, and it's likely that Behavior Trees are covered in some of these volumes. These books offer a collection of insights and techniques from different developers and researchers. Useful for gaining diverse perspectives on game AI techniques.
Is specifically tailored for those using the Unity game engine. It provides practical guidance on integrating behavior trees into Unity projects.
While this book focuses on utility theory and other mathematical approaches to game AI, it offers valuable context for understanding the decision-making processes that Behavior Trees often implement. It can help solidify the theoretical underpinnings of AI behaviors, providing a deeper understanding of why certain structures within a Behavior Tree are chosen. is useful as supplementary reading to provide a broader AI context.
While not solely focused on Behavior Trees, this widely-used textbook provides a comprehensive foundation in artificial intelligence concepts, including intelligent agents and control systems. Understanding these broader AI principles is beneficial for grasping the context and application of Behavior Trees.
Behavior Trees are often used in conjunction with or as an alternative to traditional planning algorithms in AI and robotics. provides a comprehensive treatment of planning algorithms, offering a strong theoretical background that can help in understanding the advantages and limitations of Behavior Trees in complex planning scenarios. It valuable theoretical reference.
Focuses on the fundamental algorithms in robotics, including control and vision. While not directly about Behavior Trees, it provides the necessary mathematical and algorithmic foundation for implementing the actions and conditions that constitute the leaf nodes of a Behavior Tree in a robotics context. It strong reference for the practical implementation aspects in robotics.
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