As this book was being written, the jigsaw puzzle of data from galaxies, Lyman alpha clouds, gravitational lensing and the cosmic microwave sky appeared for the first time to be coming together into a consistent theoretical model comprising a nearly flat universe with cold dark matter (CDM) and a cosmological constant. It was recognised, however, that the model leaves much to explain theoretically, especially the amount of fine tuning needed to get the desired cosmological constant. There is also a hint from gravitational lensing that the cosmological constant might be smaller than that required to explain the high redshift supernova data. CDM models produce dwarf galaxy haloes that are too numerous and too dense to be compatible with observation. There are also discussions of inflation and quantum cosmological theories of the initial conditions. The book also addresses observational issues, such as the TOCO results, the 2-degree field survey and the Sloan Digital Sky survey. Many lectures focus on the signatures in the cosmic microwave sky of various theoretical models.