If you are new to libertarianism and want a solid Primer on the foundational ideas, two classic quick reads are Economics in One Lesson by Henry Hazlitt and The Law by Frederic Bastiat.
Get the PDF ebooks of the above and more from the Foundation of Economic Education, including readings from F.A. Hayek, Leonard Read, and Ludwig Von Mises.
There is also an endless amount of free ebooks from the Mises Institute which can be found below.
And even more free ebooks from the Cato Institute.
More great beginner friendly books
For the Advanced Libertarian
If you've already read all the above books then you should have a solid foundation of libertarian concepts and their application. Below are some books that dig even deeper into how institutions effect society, how our neurology is wired for liberty, the problems with foreign aid, and immigration.
The Primal Prescription
Probably the best book available on how the healthcare system in the US evolved into the high cost monster it is, the free market solutions, and individual actions you can take to improve your life despite the system.
Click below for even more books to keep feeding your libertarian mind and empowering yourself.