Anthropogenic activities and overexploitation of plant resources have led to the deterioration/depletion of natural ecosystems, putting many tree species at risk. In this frightening situation, conservation strategies, including both in situ and ex situ, became necessary to successfully recover, restore, or reintroduce the declining phytodiversity. In vitro strategies have emerged as the most promising and efficient tools of biotechnology for germplasm conservation of various plant species, including commercially important, and rare and endangered tree species. These techniques enable the cultivation/multiplication of trees despite constraints such as limited starting material, seed dormancy, self-incompatibility, poor seed setting, and recalcitrant or non-viable seeds. Different in vitro approaches, such as slow growth for short to medium-term and cryopreservation for long-term conservation, can assist significantly in the conservation as well as reintroduction of many tree species, especially threatened species. The successful applications of slow growth and cryopreservation techniques in the conservation of tree species, recent insights, and their comprehensive compilation are presented in this chapter.