This new textbook provides a readable and accessible introduction to the subject for those students taking a first course in cosmology. An Introduction to Modern Cosmology introduces models of the expanding universe and explores all the successes of the hot big bang, including the cosmic microwave background and nucleosynthesis. A brief discussion of the inflationary cosmology is also included. No prior knowledge of astronomy is assumed and the book's general approach tends to avoid relativity, deriving the crucial results using newtonian theory. This allows a discussion of all the evidence in favour of the hot big bang in a treatment which is based in physics rather than mathematics.