One of the best introductions to Lysander Spooner is his pamphlet on Natural Law. It is an 18 page document that can be read in under 30 minutes and it provides an excellent introduction to his philosophy. Lysander states the fundamental principle of libertarian and anarchist thought succinctly as no other could.
The ancient maxim makes the sum of a man’s legal duty to his fellow men to be simply this: “To live honestly, to hurt no one, to give to everyone his due.”
Lysander Spooner – Natural Law
I hope you find it an interesting read. If you do read it, let me know what you think. It is available at the time of writing, at the following link in both HTML and PDF formats.
https://oll.libertyfund.org/title/spooner-natural-law-or-the-science-of-justice-1882