diff --git a/man7/environ.7 b/man7/environ.7
index 45f78da60..4df6a1329 100644
--- a/man7/environ.7
+++ b/man7/environ.7
@@ -138,6 +138,19 @@ or by the
 command if you use
 .BR csh (1).
 
+The initial environment of the shell is populated in various ways,
+such as definitions from
+.IR /etc/environment
+that are processed by
+.BR pam_env (8)
+for all users at login time (on systems that employ
+.BR pam (8)).
+In addition, various shell initialization scripts, such as the system-wide
+.IR /etc/profile
+script and per-user initializations script may include commands
+that add variables to the shell's environment;
+see the manual page of your preferred shell for details.
+
 Bourne-style shells support the syntax
 
     NAME=value command