The user plants roots in the ground, allowing it to restore 1/16th of its max HP at the end of every turn. This roots the user firmly in place, preventing it from escaping (unless it holds a Smoke Ball or its Trainer uses an escape item) or switching out.
Even moves that switch the target out cannot force a Pokémon under the effect of Ingrain to switch out. However, moves that switch the user out switch a Pokémon out regardless of Ingrain; additionally, a Pokémon under the effect of Ingrain can be switched out when the game allows the player to switch before an opponent sends out their next Pokémon after their previous Pokémon fainted. The effects of Ingrain can be passed by Baton Pass.
Generations IV and V
A Pokémon under the effect of Ingrain can switch out if it holds a Shed Shell. Ingrain prevents the affected Pokémon from being switched out by the Red Card, but does not affect the Eject Button.
In Red Rescue Team and Blue Rescue Team, Explorers of Time, Darkness and Sky, Ingrain causes the user to gain the Ingrain status, making the user incapable of moving (though it may attack), and cannot switch places with the team leader. The Pokémon gains 10 HP at the end of the second turn, and every five turns after that. The Ingrain status lasts 16-30 turns, but it can be cancelled prematurely by the IQ skill Wary Fighter.
In Gates to Infinity, the Ingrain status lasts seven turns and the Pokémon gains 15 HP at the end of every second turn.