A type of registration rights that confers on an investor the right to register his unregistered shares when either the invested company or other investors (shareholders) conduct a registration. That is to say, incidental rights (also known as piggyback rights) allow investors to include securities in a registration statement that the company plans to file for a primary offering or some other purpose.

So often, agreements of incidental registration rights include provisions excluding the the shares of piggyback registration holders from an ongoing offering, especially in situations where underwriters finds out that market demand is not as large as originally expected and that adding piggyback shares to the offering will have a negative effect on the share price.