ISO 14001 is the main Environmental Management System (EMS) standard which it is the equivalent of ISO 9000. This is the only standard that requires a third party assessment.
This ISO indicates to customers, business partners and competitors that your business is taking environmental issues very seriously. It indicates leadership and commitment.
The ISO 14001 requires any business to have a clear and up-to-date environmental policy, manual and procedures. The EMS has to be regularly audited, reviewed and updated. The International Organization for Standardization produced an ISO 14000 Toolkit to help you get on your way.