To ensure the organic product you are marketing to your customers meets your claims, it is important that certification processes are followed. Depending on the claims you are making and the % organic, there are a variety of certifications available:

Organic Content Standard (OCS) http://textileexchange.org/integrity/:
A voluntary chain of custody standard operated by the Textile Exchange, that provides a third party verification that product contains accurate amounts of the intended organic fibre. Certification comes as either 100% organic or blended for products that contain a minimum 5% organic content.

Global Organic Textile Standard (GOTS) http://www.global-standard.org/the-standard.html:
A product certification covering the whole textile supply chain which includes strict environmental and social criteria. The Standard requires a minimum 70% organic content and has requirements covering the remaining non-organic percentage, including accessories.

Image credit: Textile Exchange - OCS100 Standard