Yoshi, known as Mario & Yoshi in PAL regions, is a 1991 puzzle video game developed by Game Freak and published by Nintendo for the Nintendo Entertainment System and Game Boy. Both versions were first released simultaneously in Japan on December 14, 1991, and released in all other regions the following year.

In Yoshi, the player is tasked with clearing monsters from the on-screen playing field. The monsters fall in from the top of the screen to build vertical stacks; the player must prevent a stack from growing too high such that it exits the play field. In order to do so, the player swaps and moves the stacks about such that falling monsters collide with identical monsters stationed atop the stacks, causing them to be removed from play. Yoshi offers both a scoring-focused single-player mode and a competitive two-player mode.

Yoshi is a falling block game in which the player is given a playing field that is divided into four columns. The objective is to match Yoshi egg shells to hatch them and prevent the four stacks, which pile up from the falling monsters, from growing too tall. The player character, Mario, swaps the stacks around such that the falling monsters will be eliminated by coming into contact with the blocks they match.

Monsters, which consist of various Mario enemies, appear at the top of the screen and fall into each the columns, turning into blocks as they land and creating stacks that incrementally grow in height. The main objective is to prevent the four stacks from growing too high by eliminating blocks from the field; a game over occurs when any of the stacks crosses the black line drawn across the top of the play field. A stack can hold up to eight objects in the NES version or seven in the Game Boy version.

To eliminate a block from the top of a stack, it must come in contact with a falling monster that matches it. For example, if a Goomba falls directly onto a Goomba block, both will be removed. The player controls Mario, who resides below the playing field and has the ability to swap the positions of any two adjacent stacks at a time. Thus, the player is required to switch around the stacks to ensure that the monsters fall into the correct places. Points are awarded for each set of monsters that are eliminated.

In addition to the four different types of monsters, two halves of a Yoshi eggshell will also fall. The bottom eggshell half behaves like a monster: it disappears when it comes into contact with another bottom half. However, if a falling top half comes into contact with a bottom half, the two will join and hatch a Yoshi, earning the player bonus points. Furthermore, if a stack of monsters grows atop a bottom half and a top half is then added, all monsters between the halves will be encased and eliminated. Larger Yoshi characters will hatch depending on the number of monsters encased, which also increases the number of bonus points awarded. If a falling top half does not have any bottom half to join to in the stack it touches, it is automatically removed and no points are awarded.

The single-player mode has two variations: A-Type and B-Type. In A-Type, the game is played indefinitely until the player receives a game over. In B-Type, the player plays a series of levels in which the player is required to completely clear the playing field of all the blocks. The initial number of blocks inside the playing field grows as the player progresses. In multiplayer mode, a second player controls Luigi. The two players play simultaneously in separate playing fields using the traditional rules. A player wins the match by clearing all the blocks in the field or when the other receives a game over; the first player to win three matches wins overall.

Yoshi was the first collaboration between developer Game Freak and publisher Nintendo. Nintendo had previously passed on publishing Game Freak's first title, Mendel Palace for the NES. After the smaller company incorporated and began work on its second release, Smart Ball for the SNES, Nintendo made Game Freak the offer to develop Yoshi. It was suggested by Tsunekazu Ishihara, an associate of Game Freak co-founder Satoshi Tajiri, that they develop smaller games like Yoshi in order to give the company the financial backing to eventually realize its larger-scale project, the RPG series Pokémon. Yoshi was developed in six months with Tajiri as its director. Ken Sugimori came up with the gameplay concept. Ishihara and Yoshi creator Shigeru Miyamoto served as producers. Tajiri explained that it was during the development of Yoshi that he learned the "wave" design of game difficulty in which the player is presented with an easy stage directly after a challenging one to allow them to savor their accomplishment. Junichi Masuda composed the game's music and sound. Masuda stated that he spent an extensive amount of time programming the movement of the game's menu items to its music. Game Freak had also wanted to add in a realistic-sounding Yoshi voice, but Nintendo disapproved of it. In 2024, a prototype of an unreleased Nintendo DS remake was discovered as part of the October 2024 Game Freak leak, hidden in the source code of Pokémon Black and White; evidence led some to believe that the prototype may have been based on an unreleased Super Famicom version.