Statistics for An important problem in pervasive computing is how to create and maintain manageable collections of pervasive resources appropriate for disparate and typically nomadic users. This article describes physical registration, a new, human-centric mechanism for constructing collections of resources in the form of electronic directories. Users identify physical objects using sensor-equipped wirelessly networked handheld devices to build directories of virtual "entities" associated with those objects. The entities can be Web resources accessible over a network, like printers, projectors, picture frames, or storage devices. They can also be Web resources correlated with objects like books or telephones that are not themselves accessible over a network. Our article describes and motivates the method, then compares two implementations we have constructed.