diff --git a/Tutorial.md b/Tutorial.md
index 369834d..ded8843 100644
--- a/Tutorial.md
+++ b/Tutorial.md
@@ -167,9 +167,21 @@ Is that all ? Well, no, it's time to learn how to use it.
 
 # File capabilities ?
 
-Now it's time for a bit of litterature.
+Now it's time for a bit of litterature. File capabilities are unique "keys"
+associated with the files. It's used internally by Tahoe-LAFS to identify
+every file, and used as an URL to locate the file.
 
-TODO
+For immutable files, capabilities are like hash table keys, they match
+a unique file. A single bit difference between two files will give two
+different capabilities.
+
+For mutable files, there are read-only and read-write capabilities.
+A read-only capability will point to a version of a file. A read-write
+capability represant the ability to read the file, the ability to write 
+a new version of a file.
+
+for more informations, look at Capabilities section of :
+<http://tahoe-lafs.org/source/tahoe-lafs/trunk/docs/architecture.txt>
 
 # Access your shares