I have 2 activities: Main and List.
From Main you can open List; from List you can open Main.
I\'d like it so that every opening of List does not
When starting your list's Activity, set its Intent flags like so:
Intent i = new Intent(...); // Your list's Intent
i.setFlags(i.getFlags() | Intent.FLAG_ACTIVITY_NO_HISTORY); // Adds the FLAG_ACTIVITY_NO_HISTORY flag
startActivity(i);
The FLAG_ACTIVITY_NO_HISTORY flag keeps the new Activity from being added to the history stack.
NB: As @Sam points out, you can use i.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY); instead. There is no functional difference.