Tinkering with technologies and other human-made artifacts is a longstanding practice. Freedom to tinker has largely existed without formal legal recognition. Tinkering has typically taken place in an unregulated zone within which people were at liberty to act unobstructed by others so long as they did not harm others. The main reason why it now seems desirable to articulate some legal principles about freedom to tinker and why it needs to be preserved is because freedom to tinker is being challenged by some legal developments. This Article explains that user-innovators have traditionally had considerable freedom to tinker under trade secrecy, patent, and trademark laws. Although copyright law permits a modest degree of tinkering with existing products, it restricts freedom to tinker more than other IP laws. Copyright law and sometimes contract law place substantial constraints on user rights to tinker with and modify computer programs and other digital works. These constraints are ofparticular concern to tinkerers because computer programs are embedded in such a wide range of technologies these days. This Article offers suggestions about how and why the law should protect a zone offreedom to tinker for socially beneficial purposes.