The first thing to be aware of before you start to transfer your domain name from Yahoo to Gandi is that Yahoo is a domain name reseller. Your domain name is registered with a different company - so don't be surprised if you notice a different company in the “Registrar:” line of the whois.
No matter which registrar Yahoo uses for the registration of your domain, you will nonetheless perform all the administrative procedures through yahoo.
1. Begin by going to http://domains.yahoo.com
2. At the top of the page you will see a section that says “Manage your services”. Click on the button that says “Small business”.
3. Log into your account
You will now see the list of your domain names that are managed through Yahoo.
4. Find the domain name that you want to transfer to Gandi, and click on the link right below it that says “Domain Control Panel”.
5. Look down in the list of options, and you will see “Edit Domain Locking”. Click on this link.
You will now see your Domain Locking page
6. Click on the button that says “Unlock Domain”.
You will be asked to verify your intention to unlock your domain name.
7. Click on the “Unlock Domain” button on the bottom of the page.
8. Click on the “Domain Control Panel” on the upper-left hand corner to go back to your domain's control panel.
9. Scroll all the way down to the bottom of the page, and you will see a link that says “View Your Authorization Code”. Click on this link.
You will now see a table that will show you your domain name, its status, and its authorization code.
This is the code that you will need to provide to Gandi when you request the transfer from our website.
Go to http://www.gandi.net and follow our standard transfer process for domain names.
You can follow our tutorial on the procedures to transfer a domain name to Gandi at the following page of our wiki: http://wiki.gandi.net/en/domains/transfer