Paticcasamuppada explains that samsarasamsara, the process of repeated existences, is perpetuated by a chain of interconnected links of cause and effect; it also reveals the method of breaking this chain and putting an end to the process.

Dependent on avijja there arises sankhara; dependent on sankhara there arises vinnana; dependent on vinnana there arises nama-rupa; dependent on nama-rupa there arises salayatana; dependent on salayatana there arises phassa; dependent on phassa there arises vedana; dependent on vedana there arises tanha; dependent on tanha there arises upadana. Thus this vicious circle of misery rolls on. In other words, the origin of each link depends upon the preceding one. As long as this chain of twelve causal relations operates, the wheel of becoming (bhava-cakka) keeps turning, bringing nothing but suffering.
This process of cause and effect is called anuloma-paticcasamuppadaanuloma-paticcasamuppada (direct Law of Dependent Origination).
Buddha said that when any one of the links of the chain is broken, the wheel of becoming comes to an end, resulting in the cessation of suffering. This is called patiloma-paticcasamuppadapatiloma-paticcasamuppada (the Law of Dependent Origination in reverse order)