The last several years has seen an increasingly popular trend of teachers buying and selling their lesson plans and other self-created classroom materials in online marketplaces. The leader in this space is a website called Teachers Pay Teachers, which boasts 3.8 million active users. In this article, the author examines why these sites became popular and some of their key strengths, including opportunities for teachers to share classroom-tested resources, to connect with global colleagues, to make supplemental income, and to promote the teacher-prenuial spirit. The article also discusses some of the marketplaces' drawbacks, namely legal and ethical concerns, the possibility of an incoherent curriculum made up of pieced together lessons, and the lack of quality control. Still, teachers continue to use these websites, so the author provides recommendations for improving the practice of buying and selling lesson plans. The article also contains a sidebar by Andrew P. Marcinek with guidance about how to use free Open Education Resources.