Evolution is a process in which a Pokémon ascends to a more powerful and often larger form. Each evolution has one or more conditions which must be met in order for it to occur. There are many different methods of evolution, such as leveling up, using an Evolution stone on the Pokémon, or leveling up with another condition such as knowing a certain move.
Pokémon Sage introduces some new evolution methods.
29 Pokémon families do not evlolve, 57 families have 2 stages, 24 families have 3 stages, and 4 families with multiple evolution paths.