UPADANA

Upadana (clinging) and tanha (craving) are considered the two primary causes of dukkha (suffering, anxiety, dissatisfaction) in Buddhism.

Upadana means "clinging," "attachment," or "grasping," although the literal meaning is "fuel."  The Buddha identified four types of upadana:

Self-doctrine clinging.
Wrong-view clinging.
Rites-and-rituals clinging.
Sense-pleasure clinging.

They are causally interconnected as follows:

Self-doctrine clinging: first, a person assumes that he has a permanent "self."
Wrong-view clinging: then, the person assumes that he is either somehow eternal or that he will be annihilated after this life.
Rites-and-rituals clinging: if person assumes that he is eternal, then he clings to rituals to achieve self-purification.
Sense-pleasure clinging: if a person assumes that he will completely disappear after this life, then he disregards the next world and clings to sense desires.

The cessation of clinging leads to Nirvana.