Reversi

The Ultimate Guide to Reversi & Othello: Rules, Strategy, and Online Play

Welcome to the definitive resource for Reversi — also known worldwide as Othello — one of the most elegant and strategically deep abstract board games ever created. Whether you are a complete beginner learning how to play Reversi for the first time or a competitive player refining corner-based strategy, this guide covers everything from the game's 19th-century English origins to the advanced positional tactics used by world champions.

What Is Reversi? (Reversi vs Othello)

Reversi is a two-player strategy board game played on an 8×8 grid with 64 double-sided discs that are black on one side and white on the other. Players take turns placing discs on the board, and when a player "outflanks" (surrounds) one or more of the opponent's discs in a straight line, those discs are flipped to the capturing player's color. The game ends when neither player can make a legal move, and the player with the most discs of their color on the board wins.

Reversi vs Othello — What's the Difference?

This is one of the most frequently asked questions in the board game world. Reversi was invented in 1883 by either Lewis Waterman or John W. Mollett in England (both claimed credit). In 1971, the Japanese game designer Goro Hasegawa created a streamlined version with a fixed starting position and trademarked it as Othello — named after the Shakespeare play because of the thematic contrast between black and white.

The key differences:

• Starting position: In classic Reversi, the center four squares start empty and each player places two discs during the first two turns. In Othello, the four center discs are pre-placed in a fixed diagonal pattern (two black, two white).
• Branding: "Othello" is a trademarked product sold by Mattel (formerly by Tsukuda Original). "Reversi" is the public-domain name for the same fundamental game mechanic.
• Modern play: Nearly all competitive tournaments — including the World Othello Championship held annually since 1977 — use Othello rules with the fixed starting position. Online play almost universally follows the Othello convention.

On this site, we use the name Reversi with the Othello starting position, which is the standard everyone expects.

Reversi Game Specifications

How to Play Reversi — Complete Rules

Setup

The game begins on an 8×8 board with four discs placed in the center in a diagonal pattern: two black and two white. Black always moves first.

Making a Move

On your turn, you must place a disc of your color on an empty square such that it outflanks at least one of your opponent's discs. Outflanking means your new disc and an existing disc of your color form a straight line (horizontal, vertical, or diagonal) with one or more of your opponent's discs between them — with no empty squares in between.

When you place your disc, all outflanked opponent discs in every direction are flipped to your color. A single move can flip discs in multiple directions simultaneously.

Passing (Skipping a Turn)

If you have no legal move available (no placement that outflanks at least one opponent disc), your turn is automatically skipped and your opponent plays again. If neither player has a legal move, the game ends immediately — even if the board is not full.

Winning

The game ends when:

• The board is completely filled (all 64 squares occupied), or
• Neither player can make a legal move

The player with more discs of their color on the board wins. If both players have exactly 32 discs, the game is a draw.

Reversi Strategy — How to Win Consistently

Reversi is famous for the paradox of disc count: having fewer discs in the early and middle game is often better than having more. This counterintuitive principle is the foundation of all advanced Reversi strategy.

1. Corners Are King

The four corner squares (a1, a8, h1, h8) are the most valuable positions on the board. Once placed, a corner disc can never be flipped — it is permanently yours for the rest of the game. Corners also serve as anchors that let you build stable walls along the edges.

Priority: Always take a corner when it's available. Almost every winning strategy revolves around gaining corner control.

2. Avoid the X-Squares and C-Squares

The squares diagonally adjacent to corners are called X-squares, and the squares directly adjacent to corners along the edges are called C-squares. Playing on these squares is typically a serious mistake because it gives your opponent access to the corner.

• X-squares (b2, b7, g2, g7) — the most dangerous squares. Playing here almost always lets your opponent take the adjacent corner.
• C-squares (a2, b1, a7, g1, etc.) — less dangerous than X-squares but still risky, especially early in the game.

3. Maximize Mobility, Minimize Discs

One of the biggest beginner mistakes is trying to flip as many discs as possible on every turn. In Reversi, mobility (the number of legal moves available to you) is far more important than disc count during the opening and midgame.

Why? If you have many discs spread across the board, your opponent has many places to outflank you. If you have few discs concentrated in the center, your opponent has fewer options and may be forced into bad moves — including giving you corners.

4. Play for Stable Discs and Edges

Stable discs are discs that can never be flipped for the rest of the game. Corner discs are automatically stable. Discs along a full edge connected to a corner are also stable. Building a long line of stable discs is the ultimate goal of the endgame.

Edge play: Controlling edges — especially after securing an adjacent corner — creates large blocks of stable territory. A common winning pattern is to anchor two corners on the same edge and own the entire row.

5. Use Wedges and Poison Discs

A wedge is a disc placed between two of your opponent's discs on an edge, splitting their wall. This often forces them to give you a corner when they try to repair the damage.

A poison disc is a play that looks good for your opponent but actually reduces their mobility or forces them into X-squares. Advanced players deliberately create positions where every response for the opponent is bad.

6. Common Opening Strategies

Competitive Reversi players have developed named openings similar to Chess:

The Mathematics and Computer Science of Reversi

Reversi holds a unique place in the history of artificial intelligence and competitive gaming:

• Game complexity: With approximately 10²⁸ legal positions and a game-tree complexity of roughly 10⁵⁸, Reversi is vastly more complex than Checkers (10²¹ positions; solved in 2007) but simpler than Chess (10⁴⁴ positions) or Go (10¹⁷⁰ positions).
• 1980 — Moor: The first strong Reversi program, Moor, was developed by Peter Frey for early microcomputers, helping establish the game as a key benchmark for AI research.
• 1997 — Logistello: Michael Buro's Logistello program decisively defeated the reigning world Othello champion Takeshi Murakami 6–0, marking one of the earliest instances of AI surpassing a human world champion in a strategy game — even before IBM's Deep Blue defeated Kasparov in Chess.
• Modern AI: Today's strongest Othello engines like Edax and Ntest use sophisticated evaluation functions, deep search algorithms, and endgame solvers. They play essentially perfect endgames and are unbeatable by humans from about 20 moves before the end.
• Reversi is unsolved: Despite the strength of AI, Reversi/Othello has not been mathematically solved — no one knows the theoretical outcome of a perfectly played game. This puts it in the same category as Chess and Go as a game that remains computationally intractable.

History of Reversi and Othello

The history of Reversi is a fascinating tale of disputed invention, reinvention, and global competition:

• 1883: Lewis Waterman of London publishes the rules of Reversi. However, John W. Mollett claims he invented the game earlier. The dispute was never resolved, and both men are credited in different sources.
• 1888: Reversi becomes a brief fad in Victorian England, rivaling Chess in popularity among the upper classes. The German game manufacturer Ravensburger releases a Reversi set.
• 1893–1970s: Reversi fades from popular culture, surviving mainly as a niche parlor game.
• 1971: Goro Hasegawa of Japan reinvents the game with a standardized starting position and trademarks it as Othello, marketing it with the slogan "A Minute to Learn... A Lifetime to Master."
• 1977: The first World Othello Championship is held in Tokyo. Hiroshi Inoue wins the inaugural title.
• 1997: Logistello defeats world champion Takeshi Murakami 6–0, a milestone in AI history.
• 2019: Piyanat Aunchulee of Thailand becomes the youngest-ever world champion at age 11.
• Present: Reversi/Othello is played by millions online and the World Othello Championship continues annually, with participants from 30+ countries.

Reversi Variants

Glossary of Reversi & Othello Terms

• Disc (Piece) — A double-sided playing piece, black on one side and white on the other.
• Outflank — To place a disc so that opponent discs are trapped between your new disc and an existing disc of your color in a straight line.
• Flip — When outflanked discs are turned over to the capturing player's color.
• Corner — Any of the four corner squares (a1, a8, h1, h8). The most valuable squares because discs placed there can never be flipped.
• X-Square — The four squares diagonally adjacent to corners (b2, b7, g2, g7). Playing here usually gives your opponent the corner.
• C-Square — The squares directly adjacent to corners along edges (a2, b1, etc.). Risky but less dangerous than X-squares.
• Stable Disc — A disc that can never be flipped for the rest of the game. Corners are always stable.
• Mobility — The number of legal moves available to a player. High mobility is a major strategic advantage.
• Frontier Disc — A disc adjacent to at least one empty square. Frontier discs give your opponent more places to outflank you.
• Interior Disc — A disc surrounded entirely by other discs. Interior discs reduce your opponent's options.
• Wedge — A disc placed between two opponent discs on an edge, splitting their wall and often forcing a corner concession.
• Parity — In the endgame, the player who makes the last move in each empty region has an advantage. Controlling parity is an advanced technique.
• Tempo — A move that forces your opponent to respond in a specific way, giving you control of the game's pace.
• Wall — A line of stable discs along an edge, typically anchored by a corner.
• Quiet Move — A move that flips very few discs and maintains low frontier, keeping mobility high.
• Liberty — An empty square adjacent to your disc where your opponent could potentially outflank you.

Frequently Asked Questions About Reversi

Is Reversi the same as Othello?

Essentially yes. The core mechanic — placing discs to outflank and flip opponent pieces on an 8×8 board — is identical. The only difference is the starting position (classic Reversi starts with an empty center; Othello has a fixed diagonal setup) and branding. All modern competitive play and virtually all online versions use the Othello starting position, including this site.

Who goes first in Reversi?

Black always moves first in both Reversi and Othello. This gives Black a slight statistical advantage, but at the highest levels of play the difference is minimal.

What is the best opening move in Reversi?

Black's first move is always one of four equivalent positions due to the board's symmetry. The real strategic divergence begins with White's response. The Diagonal Opening (where White plays perpendicular to Black's first move) is the most common and well-studied at the competitive level. The Tiger and Rose openings are popular in tournament play.

Why is it bad to have too many discs early in the game?

Having many discs in the opening and midgame creates a large frontier — discs touching empty squares. Each frontier disc gives your opponent more potential outflanking opportunities. By keeping your disc count low and concentrated, you force your opponent into positions where they have fewer options and may be forced to play on X-squares or C-squares, giving you access to corners.

Why are corners so important?

Corner discs are permanently stable — they can never be flipped since no opponent disc can be placed behind them. Corners also anchor entire edges: once you own a corner, you can build a wall of stable discs along the edge that your opponent can never reclaim. In tournament play, the player who controls more corners wins the vast majority of games.

Can Reversi end in a draw?

Yes, but it's rare. A draw occurs when both players have exactly 32 discs each when the game ends. In competitive play, draws happen in roughly 1–2% of games.

Is Reversi a solved game?

No. Despite decades of AI research, Reversi/Othello has not been solved. The game's complexity (≈10²⁸ positions) makes complete analysis computationally infeasible with current technology. For comparison, Checkers was solved in 2007 after 18 years of computation, but Reversi is orders of magnitude more complex.

What is the highest possible score in Reversi?

The maximum possible score is 64–0, meaning one player captures every single disc on the board. This is called a "perfect game" or "wipeout." While theoretically possible, it essentially never happens between competent players.

What does "A Minute to Learn, A Lifetime to Master" mean?

This is the original marketing slogan for Othello, coined by Goro Hasegawa in 1971. It perfectly captures the game's nature: the rules are simple enough for a child to learn in minutes, but the strategic depth — involving mobility, stability, parity, and corner play — takes years to fully understand. It remains one of the most famous taglines in board game history.

How long does a game of Reversi take?

A casual game typically takes 10–20 minutes. Competitive tournament games with clocks usually allow 25–30 minutes per player. On this site, each player has 60 seconds per move, so games typically finish in 5–15 minutes.

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