There are four books which I'm pretty sure I'll never be without...

Geometry: A Comprehensive Course by Dan Pedoe

An Introduction to Differential Geometry by T. J. Willmore

Riemannian Geometry by Manfredo P. do Carmo

Topics in Algebra by I. N. Herstein

When I lost my original collection of math books, these were the first books I set out to re-acquire (except

*Topics in Algebra*, which I had with me when I lost the rest) because they cover the aspects of mathematics I find most important.

While I know most of what is covered in them (specially

*An Introduction to Differential Geometry* and

*Riemannian Geometry*), I always feel better having them within reach. And in the cases of

*Geometry* and

*Topics in Algebra*, they hold a lot of knowledge I'd really like to have a better mastery of than I currently possess.