Lumines: Puzzle Fusion (pronounced as "Loo-min-ess") is a 2004 puzzle video game developed by Q Entertainment and published for the PlayStation Portable by Bandai in Japan and by Ubisoft elsewhere. The gameplay tasks players to arrange descending two-colored 2×2 blocks to create 2×2 squares of matching color. A vertical line called the "time line" sweeps across the field, erases completed squares, and awards points. Each stage has a skin that affects the background, block colors, music, and the speed of the time line.

Lumines: Puzzle Fusion is the work of video game designer Tetsuya Mizuguchi, who had worked at Sega. Katsumi Yokota contributed to the graphic design and assisted Takayuki Nakamura with music composition. Mizuguchi originally planned a music-heavy Tetris-style game, but licensing issues led him to develop an original concept for Lumines. Mizuguchi was inspired to make a music game on the PSP, one of the few handhelds equipped with a headphone jack. The game was released as a launch title for the PSP in Japan in December 2004, North America in March 2005, and Europe in September 2005. It was later ported for mobile phones, Microsoft Windows, and the PlayStation 2 (PS2); a high-definition remaster was made for the PlayStation 4 (PS4), the Nintendo Switch, the Xbox One, Windows, and Amazon Luna.

Lumines: Puzzle Fusion sold over half a million copies in North America, Europe, and Japan, and was awarded "Best Handheld Game of 2005" by multiple media outlets. Several publications recognized it as one of the top games of 2005 and one of the best-ever launch titles. It was praised for its music and gameplay; multiple reviewers described it as addictive and drew comparisons with Tetris. The ports received less praise than the original version; critics commended the mobile phone version for its new features but criticized its poor sound quality, while the PS2 port was criticized for omitting some songs present in the original. Reviewers complimented the remastered version for enhancing the quality of sounds and visuals but were disappointed that an online multiplayer mode was not included as a new feature. The game spawned numerous spin-offs and sequels for multiple platforms, becoming the first entry in the Lumines series.

Lumines: Puzzle Fusion is a falling block puzzle game. The objective is to arrange grouped blocks descending from the top of a 16×10 grid playing field to create single-color squares once they have landed. Grouped blocks have a 2×2 shape and vary between two colors. Players can rotate the descending grouped blocks, move them left or right, or drop them straight down. When part of the grouped blocks hits an obstruction, the remaining blocks separate from the rest and continue to fall. A single-color square is created when grouped blocks form a 2×2 shape of matching color. Additional blocks of matching color can be used to create larger shapes. The game ends when the blocks pile up to the top of the playing field.

A vertical line known as the "time line" sweeps through the playing field from left to right, erasing any completed single-color groups of blocks it touches and awarding points for each group. If a square is formed while the time line is passing, the portion it intersects is cleared with no points are awarded. Players earn increasing score multipliers by repeatedly clearing squares on consecutive time line sweeps. Additional score bonuses are earned by clearing the playing field or reducing the remaining blocks to a single color. The maximum score is 999,999 points. Blocks with embedded gems are known as "special blocks"; if these are used to create squares, they allow the time line to eliminate adjacent blocks of the same color. Each stage has a skin that affects the background's appearance, the blocks' color scheme, the music track, sound effects, and the speed of the time line. Stages with fast tempos make it more difficult to create large combos, while slow tempos can cause the playing field to fill more quickly.

Lumines: Puzzle Fusion has five modes: Challenge, Single Skin, Time Attack, Puzzle, and Versus. Challenge mode is the main mode and cycles through skins in a fixed order of increasing difficulty. Single Skin mode allows players to select one skin to play for the entire session. In Time Attack mode, players have a limited time to clear as many blocks as possible. Puzzle mode challenges players to arrange blocks to create pictures. In Versus mode, players battle against A.I. opponents or against other players via wireless connections. The Versus mode begins with the playing field divided in half; the goal is to clear successive squares, which shrinks the opposing player's space.

Later ports and remasters added modes such as Arcade, Mission, Shuffle, and Skin Edit mode. Arcade mode is designed for mobile phone ports; players complete a total of 10 stages with CPU versus battles serving as Boss stages after a certain amount of stages are complete. Arcade mode adds blocks that can explode, a third color block within certain stages, and new grouped block shapes such as S-shaped or three-block-wide rectangles. Mission mode tasks players with challenges such as clearing the stage in a certain number of moves or clearing a specified number of columns. Shuffle mode creates game sessions with randomized order of stages. Skin Edit mode allows players to customize their game session by selecting the order of unlocked skins.

Lumines: Puzzle Fusion was the first game developed by Q Entertainment with Tetsuya Mizuguchi as the designer. Mizuguchi was part of the studio's founding following his departure from Sega after they dissolved United Game Artists, Mizuguchi's previous venture. It was developed by six people in a year. The game was 75% complete when it was announced at the Tokyo Game Show 2004. When he first learned about the PlayStation Portable (PSP), Mizuguchi was inspired to make a puzzle game with music for the device, which he described as an "interactive Walkman". He considered it ideal for his game because it was one of the few handheld consoles to have a headphone jack and high-quality sound. To attract casual players, Mizuguchi wanted his new game to be less daunting to play than his earlier titles Rez and Space Channel 5. Originally, he wanted to make a music-heavy Tetris-style game but problems with licensing led him to create a new concept. Mizuguchi did not consider developing games for the PSP difficult and began working on the game before any PSP software tools were provided. The game's title was derived from "Lumine", meaning to illuminate. The subtitle "Puzzle Fusion" is intended to reflect the mixture of music and gameplay.