These lectures focus on the methods of observational cosmology and their physical basis. After a brief reminder of the essential elements of the Big Bang model, we look at some of the basic methods for surveying the homogeneous universe. The second half of the lectures examines the perturbed universe - large-scale structure and the cosmic microwave background anisotropies. In the last few years we have seen the emergence of a ``standard'' cosmological model with coherent parameters. The goal of the course is to understand the rather vast array of observational approaches used to establish and test this model in detail.