H1 Transfer

The buzz word for everyone who lands in USA with a H1 visa is "VISA TRANSFER". Which simply means that if a candidate wants to change his employer, he can simply go for a visa transfer and start working for a new employer.
Frankly speaking there is nothing called VISA TRANSFER in books of USCIS.
It all started with American Competitiveness for the 21st Century Act (AC21). According to this, a candidate on legal H1B employment visa status may lookout for a change of job through another employer provided new employer has filed a petition on behalf of the foreign national. The cost of this new petition will be same as a new Filing, however there is no need for a person to move out of country for change of employer, He can start his association with the new employer once the receipt of the petition by USCIS, which take approximately 3 working days. The new employer can file for the extension of H1 period while filing of petition. However the maximum stay on H1 will remain 6 years irrespective of the number of employers the candidate shifts.
Now the question is what happens to the old petition, The answer is, old petition is still valid, unless the old employer chooses to revoke the Petition. All valid petitions are mutually exclusive, which means if the candidate is holding valid petition with company A and has transferred his employer to company B and started working with B, then company A petition will be automatically be void.
Please note the candidate can get back to his old employer any time start working with him if the old petition is still valid.
List of documents required for transfer of H1:

Latest resume;
Two to three latest pay slips
Copy of existing Complete H1B packet
Photocopy of your existing valid visa
Copy of valid passport
I-94 copy
Diploma/Degree certificate and transcripts
Copy of your social security card

New employer files the petition using the above documents and as said earlier, the cost of filing is same as filing a new application. Candidate can start working with the new employer once the receipt of application by USCIS.
If by any Chance the application request is denied, then the candidate looses his VISA as well and has to move out of the country immediately.