diff --git a/index.md b/index.md
index eadcf84e..0c8536e5 100644
--- a/index.md
+++ b/index.md
@@ -12,7 +12,7 @@ site: sandpaper::sandpaper_site
 
 ## Prerequisites
 
-This lesson requires a basic knowledge of the MARC21 standard.
+This lesson requires a [basic knowledge](https://www.loc.gov/marc/96principl.html) of the [MARC21 standard](https://www.loc.gov/marc/).
 
 
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