The foundations of our present understanding of the universe as a whole, both theoretical and observational, were laid down in the period 1917–1929. The last few years have seen developments of almost equal importance, again both theoretical and observational. In these circumstances I prefer not to emphasize the historical context, but to concentrate on the leading features of our present conception of the universe, with historical aspects entering only incidentally. I shall also avoid giving a detailed critical account of the relevant observational data since that would not be in the spirit of this conference. However it must be recognized that observational astronomy is far less reliable than experimental physics, and that, with one notable exception, cosmological data are amongst the least reliable in astronomy. Indeed at the present moment we are passing through a particularly controversial period, when even the standard interpretation of red shifts is being seriously challenged. To avoid prolixity I shall confine myself to the conventional attitude on these controversial questions, but I give a general warning that we lack any crucially convincing evidence. It seems likely that such evidence will be discovered when satellite astronomy gets into its stride.