Power source: Primal
The shaman's role in the party is generally similar to that of the Cleric. The shaman has access to healing and defensive powers, though not always at the same level as the Cleric does. The shaman list of spells (or powers in 4e) differs from the cleric's list in that it often specifically addresses more natural phenomena, like the druid's spell list.
The chief difference is the shaman's spirit companion, adding a different layer of complexity to combat in 4e.