Ruminants play an important role in supplying human nutritional requirements. Given the increasing number of livestock and the limited resources to supply feedstuffs in order to feed ruminants, scientists are seeking ways to add to the ruminants’ diets parts of trees and shrubs and to replace concentrates competitive with human food. A consequent positive result could be reduction of the costs for meat and milk yield. On the other hand, these feeds could contain some anti-nutritional factors such as tannins that can limit their use. In this paper, the use of components of some trees and shrubs as part of ruminant (cattle, sheep and goat) diets as well as their positive and negative effects on domestic animal productivity are reviewed.