These lectures where designed to give the student the reasoning behind relativity. Unlike some books, this book does not just explain the results or phenomena of relativity. Feynman actually explains the problems with Newton's laws and actually derives and gives the reasoning for Einstein's theories about relativity. These lectures need only some calculus and basic physics knowledge to appreciate. However, as with most bonfide scientific literature, the more "mathematically and scientifically mature" the reader the better. Feynman uses pieces of calculus (very basic stuff), algebra (symmetry, vector notation, cross products, and dot products), geometry (non-Euclidian), and basic physics knowledge (conservation laws, Newton's laws, Maxwell's equations etc). You don't need all of this to listen and understand the lectures, but obviously the more the better. Feynman also does a good job of explaining some the mathematics involved as well. The lectures pretty much follow the book so you can read along while you listen. These are actual lectures that Feynman gave at Caltech to undergraduates so they are very rigorous. In short, the lectures were clear, very understandable, and offer something to everyone. You don't need anything more than a solid background in calculus and introductory physics to get something out of these lectures.