A certification scheme is essentially a programme used by a business to illustrate its credentials.  For example, a star rating is certification for quality.  In sustainability terms certification should ensure that a business is operating sustainable practices within their business.  Sustainability schemes, or Green Schemes/Eco Labels as they are also known vary significantly in their style from simple self assessment approaches to third party certification, where an assessor will call.  Each of them can help a business understand what is involved in "going green" but the assessed varieties are the best in terms of giving additional advice and providing confidence to market a business as being Green to consumers.