Clojure is a robust, practical, and fast programming language with a set of useful features that together form a simple, coherent, and powerful tool.

The Clojure Programming Language

Clojure is a dynamic, general-purpose programming language, combining the approachability and interactive development of a scripting language with an efficient and robust infrastructure for multithreaded programming. Clojure is a compiled language, yet remains completely dynamic – every feature supported by Clojure is supported at runtime. Clojure provides easy access to the Java frameworks, with optional type hints and type inference, to ensure that calls to Java can avoid reflection.

Clojure is a dialect of Lisp, and shares with Lisp the code-as-data philosophy and a powerful macro system. Clojure is predominantly a functional programming language, and features a rich set of immutable, persistent data structures. When mutable state is needed, Clojure offers a software transactional memory system and reactive Agent system that ensure clean, correct, multithreaded designs.

I hope you find Clojure's combination of facilities elegant, powerful, practical and fun to use.

Rich Hickey
author of Clojure and CTO Cognitect

Companies Succeeding with Clojure

“Our Clojure system just handled its first Walmart black Friday and came out without a scratch.”
Anthony Marcar, Senior Architect
Walmart Labs
“Clojure is a functional programming language from top to bottom. This means that code written in Clojure is very modular, composable, reusable and easy to reason about.”
Chris Price, Software Engineer
Puppet Labs
“We discussed the existing Clojure community, the maturity of the language itself and the momentum we saw in the industry. Companies are seeing speed to market deliveries ... based on Clojure.”
Dave Elliman, Head of Technology

Read more about Clojure success stories, how the community uses Clojure, and find companies using Clojure.


Clojure has a set of useful features that together form a simple, coherent, and powerful tool.

Dynamic Development

Clojure is a dynamic environment you can interact with. Almost all of the language constructs are reified, and thus can be examined and changed. You can grow your program, with data loaded, adding features, fixing bugs, testing, in an unbroken stream.

Functional Programming

Clojure provides the tools to avoid mutable state, provides functions as first-class objects, and emphasizes recursive iteration instead of side-effect based looping. Clojure is impure, yet stands behind the philosophy that programs that are more functional are more robust.


Clojure is a member of the Lisp family of languages. Many of the features of Lisp have made it into other languages, but Lisp's approach to code-as-data and its macro system still set it apart. Additionally, Clojure’s maps, sets, and vectors are as first class in Clojure as lists are in Lisp.

Runtime Polymorphism

Systems that utilize runtime polymorphism are easier to change and extend. Clojure offers simple, powerful and flexible mechanisms for runtime polymorphism. Clojure’s protocols and datatypes features add mechanisms for abstraction and data structure definition with no compromises vs the facilities of the host platform.

Concurrent Programming

Clojure simplifies multi-threaded programming in several ways. Because the core data structures are immutable, they can be shared readily between threads. Clojure, being a practical language, allows state to change but provides mechanism to ensure that, when it does so, it remains consistent, while alleviating developers from having to avoid conflicts manually using locks etc.

Hosted on the JVM

Clojure is designed to be a hosted language, sharing the JVM type system, GC, threads etc. All functions are compiled to JVM bytecode. Clojure is a great Java library consumer, offering the dot-target-member notation for calls to Java. Clojure supports the dynamic implementation of Java interfaces and classes.

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Cognitect is a collection of experienced, thoughtful technologists, passionate about helping organizations deploy technology effectively and humanely to build better futures.

In addition to working directly with companies to deliver innovative solutions, Cognitect offers architectural review, training and talent development services for companies and teams deploying Clojure and ClojureScript.

Cognitect are also the makers of Datomic, a transactional database with a flexible data model, elastic scaling, and rich queries. Datomic Ions let you develop Clojure applications for AWS by deploying your code to a running Datomic cluster.

“We have created some of the sharpest tools in the business. We believe this platform is a better way to develop software, and we want you to have confidence using and deploying these tools. Open source doesn't mean you're on your own any more.” –