Delve into the foundations of cosmological perturbation theory in this comprehensive lecture by David Wands from the International Centre for Theoretical Sciences. Explore the history of the universe, analyze ESA Planck CMB maps and power spectra, and examine the composition of the cosmos today. Learn about Einstein's theory of general relativity, Friedmann's dynamic cosmology, and the FLRW metric. Investigate scalar, vector, and tensor perturbations, Fourier transforms, statistical distributions, and power spectra. Gain insights into expanding and perturbation equations order-by-order, higher-order statistics, and metric perturbations. Conclude with a Q&A session to reinforce understanding of these complex cosmological concepts.