Delve into the intricacies of cosmological perturbation theory in this comprehensive lecture by David Wands from the International Centre for Theoretical Sciences. Explore key concepts such as metric perturbations, gravitational waves, and vector perturbations. Gain a deep understanding of scalar metric perturbations and their geometrical interpretation. Examine gauge dependence, linear gauge transformation rules, and various gauge-invariant variables. Learn about different gauges including longitudinal, comoving-orthogonal, uniform-density, and spatially-flat. Investigate energy-momentum conservation and the relationships between gauge-invariant variables. Conclude with a Q&A session to reinforce your understanding of these advanced cosmological concepts.