You first meet Yoshi in "Super Mario RPG: Legend of the Seven Stars" once you make it to Yos'ter's Isle. You get to help Yoshi win a race against Boshi, the blue Yoshi dude with shades and spikes. Once you do, you have Yoshi's friendship for the rest of the game. You can call on him with Yoshi Cookies to help him defeat your enemies. Also, you can come back to Yos'ter's Isle anytime to have fun racing and placing a few wagers! See what happens if you keep feeding the baby Yoshi cookies throughout the game...
For a more complete list of the video games you can catch Yoshi in, check out Yoshi's Game-ography
