The article discusses the features and main stages of rare and endangered plant species introduction. It is necessary to be guided by the principles of priority and expediency in the preparatory stage, which includes the analysis of literary data and preliminary studies in nature. The first stage is the primary introduction; it involves a detailed study of natural populations and organizing an introduction site. Based on the obtained results, the acclimatization assessment is determined. The study of biological features including reproduction is carried out at the second stage. The third stage includes investigations of the introduced populations. The phenorhythm stability, limiting factors determining dates of phenophase onset, the introduction population optimal size and number, seed longevity and conditions of their storage, self-maintenance ability are revealed. As a result, it is given the adaptation assessment, and recommendations are developed to save rare and endangered species in nature and under introduction conditions. Additional studies include applying karyological, molecular-genetic, biotechnological techniques, and possibilities to reconstruct natural populations.