Gravitational lensing occupies a central role in astrophysics and cosmology. Addressing some of the most pressing scientific issues, this unique monograph provides a rigorous, unified, exposition of gravitational lensing in spacetimes with matter (ordinary and dark matter), cosmological constant and evolving dark energy, and black holes. Emphasis is placed on the rigorous analytical aspects of the subject, while at the same time introducing general relativity. This work can be used as a text for a graduate level course or advanced undergraduate seminar in General Relativity or Gravitational Lensing. The work is interdisciplinary and should be of interest to researchers in mathematics, mathematical physics, astrophysics, cosmology, and general relativity.