Summoner Mastery

The Mastery is the way that a summoner is able to focus their intense magical training into three specific categories, which collectively are known as masteries. Some of the more advanced masteries require not only a working knowledge of previous masteries within a single category, but also the knowledge of a specific mastery. As a summoner gains levels of power within the League of Legends, they are able to select which specific areas of interest to focus on.

Summoner masteries are not set in stone; based on the type of champion you wish to control in a battle arena, masteries can be changed to better suit a summoner's needs, simply by pressing the "Return Points" button to completely reset your masteries and allow yourself to choose others in which to spend your points ("re-spec").

Attainment
With each level that a Summoner gets, the Summoner also gains one mastery point. Thus, with the current maximum level of 30, one is able to use 30 mastery points at their best. Each mastery takes one point to increase its level and each tree contains a total of 31 points worth of masteries, so even at top level the Summoner is not quite able to completely fill any one tree, let alone all trees. This adds a strategic element to your selection of Summoner masteries, as you can choose masteries that synergize with your champion, spells, and teammates.

It is important to note that most masteries require points in other masteries earlier in the tree. When moving to higher levels in the tree (higher "tiers"), one will encounter an increasing prerequisite of a 4 points spent in that tree. For example, in order to put points into Awareness (a tier-2 utility mastery), one must first put a total of 4 points into any of the tier-1 utility masteries, and to put a point into Tenacity (the tier-6 defense skill), one must have 20 points in other defense masteries.

Another, more direct type of prerequisite is shown by the grey lines that sometimes lead from one mastery to another higher-tiered mastery. These lines denote the fact that the earlier mastery must fully acquired ("maxed out") before the higher-tiered mastery will become available.

Trees
There are three types of trees that your summoner can develop in:
 * Offense Mastery
 * Defense Mastery
 * Utility Mastery