Migrating Users from Older Versions of Drupal I'm part of a team that's going to be migrating several older Drupal sites (Drupal 5, Drupal 6) into a new, single Drupal 7 site.  I'm familiar with Drupal from a software architecture point of view, but not as familiar with the day to day running of a Drupal site as I'd like.  Because of this I have a few general questions about this migration. 

Are Drupal's password hashing mechanisms consistent across different versions?

If not, are there tools to support migrating user accounts and converting the passwords between versions?

If a no to migrations, are there modules that provide a standard experience for this situation that allows an old user to pick a new password?
Are Drupal's password hashing mechanisms consistent across different versions?

No, D7 and D8 use SHA512 with a salt. Drupal 6 uses MD5 without a salt.

If not, are there tools to support migrating user accounts and converting the passwords between versions?

Yes you can just rehash them.

If a no to migrations, are there modules that provide a standard experience for this situation that allows an old user to pick a new password?

Yes there is a really simple way (one example is). Make sure you BACKUP before you do anything. If this does not work for you, google how to convert drupal 6 passwords to drupal 7. There is a ton of different ways.

&lt;?php
        require_once DRUPAL_ROOT . '/' . variable_get('password_inc', 'includes/password.inc');
        $res = db_query('select * from drupal.users');

        if($res) {
                foreach ($res as $result) {
                        $hashed_pass = user_hash_password($result-&gt;pass, 11);
                        if ($hashed_pass) {
                          $hashed_pass  = 'U' . $hashed_pass;
                          db_update('users')-&gt;fields(array('pass' =&gt; $hashed_pass))-&gt;condition('uid', $result-&gt;uid)-&gt;execute();
                        }
                }
        }