A Greenshoe Option is an over-allotment option. In the context of an initial public offering (IPO), it is a provision in an underwriting agreement that grants the underwriter the right to sell investors more shares than initially planned by the issuer if the demand for a security issue proves higher. Here's how to create a greenshoe option for your products.The greenshoe option is a provision in an underwriting agreement that grants the underwriter the right to sell investors more shares than initially planned by the issuer if the demand for a security issue proves higher than expected. It's similar to the rights (or "option") an option trader has to buy or sell more shares than they planned to buy or sell.