In addition to its immense environmental benefits, the great expansion of wind energy generates simultaneous concerns about its adverse impacts. The impacts have been identified for human populations, landscape and wildlife, but, due to direct fatality, birds and bats are the groups for which scientists are most concerned. Due to renewable energy goals, Portugal has witnessed a great development of wind energy in recent years, with a substantial part of its mountainous areas occupied by on-shore wind turbines. In this chapter we present a literature review on the major impacts that wind energy has on birds and bats, but also in terrestrial mammals, because of the evidence of disturbance and/or displacement of more sensitive species, mostly during the operation phase. Despite there are few published data, we focus the research on Portuguese examples. Some considerations of evaluation of the impacts and cumulative impacts are also made.