Lisp vs Clojure: which is better for functional development?

Clojure fits modern, concurrent, JVM-based functional development better than Common Lisp for most new projects, because Rich Hickey designed it in 2007 around immutable data structures and concurrency rather than adding those on later. Common Lisp still fits projects that need direct system control, a mature standard, or an existing Lisp codebase.

When does Common Lisp fit better?

Common Lisp fits when a project needs low-level control over execution, an existing codebase already runs on it, or the team relies on the Common Lisp Object System for object-oriented extensions alongside functional code. It has been standardized since 1994 as ANSI X3.226, giving it a stable, well-documented core that predates Clojure by more than a decade.

When does Clojure fit better?

Clojure fits projects that need concurrency handled safely by default. It runs on the JVM, uses immutable persistent data structures, and provides software transactional memory so multiple threads can update shared state without manual locking. For teams already working in a JVM environment, it also interoperates directly with existing Java libraries.

What's the practical difference day to day?

Common Lisp gives more control over how memory and execution work but leaves concurrency and immutability to the programmer's own discipline. Clojure removes that burden by making immutability the default and building concurrency primitives into the language, at the cost of running on the JVM and inheriting its startup time and memory model.