As your characters gain experience in battles, they are assigned Ability Points (AP) from time to time. Characters must participate in a battle (i.e. attack or heal) as well as remain standing at the completion of the battle in order to be credited with participation. The AP can be "spent" to move about on the Sphere Grid, which is a set of interconnected honeycomb like circles containing 859 skill update nodes, plus many more, which just occupy space.

All of the nodes are initially ghosted. Each playable character is assigned a portion of the grid. You can access each character's portion of the Sphere Grid by first pressing the 'Triangle' button, then selecting a character's name, and finally choosing "Sphere Grid" from the top right entry on the main menu. Some nodes can only be unlocked with spheres found in chests or obtained by talking with non-player characters.

Since more than one character can "claim" an individual node, a method of skill ownership differentiation is required. Seven different colors are used to represent the playable characters' node ownership on the grid. Tidus' is Aqua, Yuna's is White, Auron's is Red, Kimahri's is Indigo, Rikku's is Green, Lulu's is Purple, and Wakka's is shown in Yellow. You must have the cursor on or adjacent to the node you wish to activate and your inventory must contain the required activation sphere in order to be able to activate the desired node.