Tightly connect tubes used for the circulation of cryogenic fluids is a task that requires some thought and technical experience. ESO is intensively using liquid nitrogen either to pre-cool large infrared instruments or to keep most of the optical and some IR detectors at cryogenic operating temperature. A solid experience has been gained with many applications for which solutions have been developed and improved over the years. The paper analyses the various types of connection and presents technical solutions which have proven to be very reliable.