diff --git a/03_how_ln_works.asciidoc b/03_how_ln_works.asciidoc
index c8180ef..527d5e9 100644
--- a/03_how_ln_works.asciidoc
+++ b/03_how_ln_works.asciidoc
@@ -96,7 +96,7 @@ Payment channels have a few very interesting and useful properties:
 
 
 Bitcoin was about five years old when talented developers first figured out how payment channels could be constructed and by now there are at least three different methods known.
-This chapter will focus on the channel construction method first described in the Lightning Network whitepaper by Joseph Poon and Thaddeus Dryja in 2015. These are known as _Poon-Dryja_ channels, and are the channel construction method currently used in the Lightning Network.
+This chapter will focus on the channel construction method first described in the https://lightning.network/lightning-network-paper.pdf[Lightning Network whitepaper] by Joseph Poon and Thaddeus Dryja in 2015. These are known as _Poon-Dryja_ channels, and are the channel construction method currently used in the Lightning Network.
 The other two proposed methods are _Duplex Micropayment_ channels, introduced by Christian Decker around the same time as the "Poon-Dryja" channels and _eltoo_ channels, introduced in 2018 by Christian Decker, Rusty Russel and (author of this book) Olaoluwa Osuntokun.
 
 Eltoo channels have some interesting properties and simplify the implementation of payment channels. However, eltoo channels require a change in the Bitcoin scripting language and therefore cannot be implemented on the Bitcoin mainnet as of 2020.