Tonglen

Tonglen (Tib. gtong len) - The practice of "giving" (tong) and "receiving" (len), it is part of the instruction on 'mind training' (Tib.lojong) brought to Tibet by Lord Atisha. In this practice one gives one's happiness and its causes to others while receiving or absorbing other's suffering; is referred to in the seventh of the Eight Verses of Training the Mind.

His Holiness the Dalai Lama says :

To be able actually to transfer one's happiness to others and directly take their sufferings upon oneself is something only possible on a very, very few occasions; it occurs when oneself and another individual have a very special type of relationship based on karmic affinity stemming, perhaps from a previous life. Then why does one cultivate this attitude? Because it leads to attaining great strength of character, courage and enthusiasm; and improves one's own practice of developing bodhichitta

Geshe Chekawa says:

Giving and receiving should be practiced alternately. This alternation should be placed on the medium of the breath.