Introduction Definition and Objective of Acclimatization Definition Objective of Acclimatization and Steps for Achieving the Objective General Characteristics of the In Vitro Environment Environmental Factors Affecting the Growth and Development of Plants In Vitro Aerial Environment Root Zone Environment Responses of Plants to the In Vitro Environment Ex Vitro Acclimatization and General Responses of Plants in Conventional Micropropagation Reasons for the Difficulty of Ex Vitro Acclimatization in Conventional Micropropagation Trophic Phases—Heterotrophy, Photomixotrophy, and Photoautotrophy Photosynthetic Ability, CO2 Concentration in Culture Vessel, and Net Photosynthetic Rate of Plants In Vitro Reason for High Relative Humidity In Vitro Conventional and Future Approaches for Acclimatization Environmental Control Unit for the Ex Vitro Acclimatization In Vitro Acclimatization Relative Humidity CO2 Concentration Photosynthetic Photon Flux Supporting Material Use of Mycorrhizal Fungi and Bacteria A Temporary Root Zone Immersion Bioreactor for Photoautotrophic Growth and In Vitro Acclimatization of Somatic Embryos Advantages of Photoautotrophic Micropropagation Acclimatization in Future Micropropagation Systems Bibliography