Renju

Renju is a two‑player abstract strategy board game that evolved from gomoku. It is played on a 15×15 grid with black and white stones. The objective is to align five stones in a row while preventing the opponent from doing the same.

Unlike free‑style gomoku, Renju incorporates a set of rules to balance the first‑player advantage. These include the prohibition of overline, two‑faced lines, and certain win patterns. The game is played in alternating turns, with black moving first, and uses a formal drawing technique for won positions.

A key feature is the use of a referee or automated system to flag illegal moves, particularly the forbidden openings known as illegal patterns such as the 3‑3, 4‑4, and 5–5 openings. These rules are codified in the Renju Association's official guideline, ensuring fair play.

Internationally, the World Renju Federation organizes the World Renju Championship every two years, with national associations selecting players through qualifying tournaments. The game enjoys a strong presence in East Asia, notably Japan, China, and South Korea, and has a dedicated following in Europe.

Computer research has produced strong Renju programs like NanJing1 and November. While artificial intelligence has yet to dominate, the field has advanced strategic understanding of patterns and opening theory. Scholarly literature, such as the Renju Opening Handbook, provides exhaustive databases of legal positions.