After decades of likely absence, wolves were reintroduced to Yellowstone National Park on January 12, 1995. This reintroduction began one of the most successful wildlife reintroduction programs in the US.  Since 1995, wolves in Yellowstone have been tracked and studied, while the impact on plant and animal life could now be quantified. This also provides valuable lessons for other animal reintroduction efforts that attempt to re-balance fauna and between predator and prey.