The history of introduction of sika deer to continental Europe is reviewed and their acclimatization to the local environment is summarized in this chapter. Besides free-ranging feral populations, there is an unknown number of captive-bred sika. With growth of deer farming in Europe, the interest in this breeding of sika increase. Sika appear to be successful competitor with local deer species and, in addition, can migrate long distances and lone individuals can join red deer. Imported sika occasionally interbred with other deer species. Disregard of hybridization has resulting in introgression of sika and red deer genes. Still, there is no wildlife management strategy in continental Europe to solve the situation, and free-ranging sika population further increase in numbers.