Lisp is not a single language but a family of dialects sharing fundamental syntax. Beginners often ask which dialect to learn first; the answer matters less than learning Lisp's new programming paradigm. Once you master one dialect, switching is relatively easy.

Common Lisp (CL), standardized by ANSI in 1994, is the most mature and comprehensive dialect. Its most famous implementation, SBCL, compiles to native code with performance comparable to C and Rust. CL provides extensive built-in functionality: compilation control (COMPILE, EVAL), machine-code inspection (DISASSEMBLE), and a powerful condition/restart system for debugging live processes. It supports multiple paradigms including functional, imperative, and object-oriented programming via CLOS, featuring multiple dispatch and generic functions. Dynamic typing with optional type declarations adds flexibility.

CL excels in long-running processes, research prototyping, and startups needing rapid adaptation. It powers quantum computing at Rigetti Computing, core services at Grammarly, and Google Flight Search. Paul Graham originally wrote Hacker News in Arc; today it runs on Clarc, a Common Lisp implementation serving 10 million pages daily. Learning resources include *Practical Common Lisp* by Peter Seibel and *A Road to Common Lisp* by Steve Losh, with Emacs + Slime as the preferred IDE.