Defensive design is a design technique used to prevent contingencies from occurring in the use of devices, objects, procedures or routines. It seeks to prevent the end user from causing failures due to not knowing the proper way to use or execute, preventing them from having more than one way of doing things. The origin of this technique is found in Murphy's Law.

At the time of designing, the study is carried out of the different ways in which the procedure, object or device can be poorly performed or executed; and mechanisms are developed so that these incorrect ways cannot be carried out, forcing correct use or execution.

Common examples of the results of this technique are seen in some connectors, where the plug and socket are designed in such a way that they can only be connected in one way, such as USB and Firewire.