The quest for knowledge and the initiative to solve the mysteries around us entail to develop instruments at the state of the art in many technological domains. This is particularly true in the field of astrophysics, where the signals from faint galaxies and other dim sources require to use high sensitivity leading experiments. In that respect cryogenics and the use of low temperature detectors are often essential for the accomplishment of the scientific objectives, offering unique advantages and unmatched performance. Therefore there is an increasing demand for coolers able to provide temperature below 1 K. Cooling for space implies specific requirements such as operation in microgravity, limited energy and mass budgets, reliability and long lifetime. These last two requirements also apply for systems dedicated to ground-based telescopes, usually set in remote and harsh environment such as the high altitude Atacama site in Chile or south pole, for which maintenance must be limited to a strict minimum. Various solutions have been successfully developed and flown, or are currently in operation in ground based telescopes. New developm ... mehrents are underway. Several cooling techniques and projects will be presented and discussed.