Cosmic dust particles play an important role for the thermal, dynamical and chemical conditions in many astrophysical environments, especially for the star and planet formation process and the late stages of stellar evolution. Dust particles determine the spectral appearance of protostars as well as evolved stars with circumstellar envelopes, and they also dominate the extinction curves of galaxies. The most efficient site of dust formation in the present universe is the cool extended atmospheres of carbon-rich and oxygen-rich AGB stars. Dust production also seems likely to occur in supernova remnants, especially in the early universe, however, the true nature of such supernova dust is not as well described as for AGB stars either observationally or theoretically. Once the dust is formed it will enter the interstellar medium and be an important ingredient for further star- and planet-formation. During star-formation, dust seems to be an important coolant which can lower the temperature in the centre of the molecular clouds and thereby lead to the formation of smaller stars than in a non-dusty cloud. If the star is formed with an accretion disk containing dust grains, the subsequent planet-formation will occur more effectively than in a dustless disk.