Erlang (/ˈɜːrlæŋ/ UR-lang) is a general-purpose, concurrent, functional high-level programming language, and a garbage-collected runtime system.

[7] The sequential subset of the Erlang language supports eager evaluation, single assignment, and dynamic typing.

[13] The initial version of Erlang was implemented in Prolog and was influenced by the programming language PLEX used in earlier Ericsson exchanges.

[14] According to co-inventor Joe Armstrong, the language went from laboratory product to real applications following the collapse of the next-generation AXE telephone exchange named AXE-N in 1995.

[8] In February 1998, Ericsson Radio Systems banned the in-house use of Erlang for new products, citing a preference for non-proprietary languages.

Erlang processes can be seen as "living" objects (object-oriented programming), with data encapsulation and message passing, but capable of changing behavior during runtime.

"[19] In 2014, Ericsson reported Erlang was being used in its support nodes, and in GPRS, 3G and LTE mobile networks worldwide and also by Nortel and Deutsche Telekom.

As Tim Bray, director of Web Technologies at Sun Microsystems, expressed in his keynote at O'Reilly Open Source Convention (OSCON) in July 2008: If somebody came to me and wanted to pay me a lot of money to build a large scale message handling system that really had to be up all the time, could never afford to go down for years at a time, I would unhesitatingly choose Erlang to build it in.Erlang is the programming language used to code WhatsApp.

Elixir is a programming language that compiles into BEAM byte code (via Erlang Abstract Format).

[22] Since being released as open source, Erlang has been spreading beyond telecoms, establishing itself in other vertical markets such as FinTech, gaming, healthcare, automotive, Internet of Things and blockchain.

Such hierarchies can exist to arbitrary depths and have proven to provide a highly scalable and fault-tolerant environment within which application functionality can be implemented.

Erlang is conceptually similar to the language occam, though it recasts the ideas of communicating sequential processes (CSP) in a functional framework and uses asynchronous message passing.

In 2005, a benchmark with 20 million processes was successfully performed with 64-bit Erlang on a machine with 16 GB random-access memory (RAM; total 800 bytes/process).

While threads need external library support in most languages, Erlang provides language-level features to create and manage processes with the goal of simplifying concurrent programming.

A message may comprise any Erlang structure, including primitives (integers, floats, characters, atoms), tuples, lists, and functions.

It also includes a native code compiler on most platforms, developed by the High Performance Erlang Project (HiPE) at Uppsala University.

[37] It also supports interpreting, directly from source code via abstract syntax tree, via script as of R11B-5 release of Erlang.

In 1998, Ericsson released Erlang as free and open-source software to ensure its independence from a single vendor and to increase awareness of the language.

[38] Although Erlang was designed to fill a niche and has remained an obscure language for most of its existence, its popularity is growing due to demand for concurrent services.