We describe the algorithmic design of a worldwide location service for dist
ributed objects. A distributed object can reside at multiple locations at t
he same time, and offers a set of addresses to allow client processes to co
ntact it. Objects may be highly mobile like, for example, software agents o
r Web applets. The proposed location service supports regular updates of an
object's set of contact addresses, as well as efficient look-up operations
. Our design is based on a worldwide distributed search tree in which addre
sses are stored at different levels, depending on the migration pattern of
the object. By exploiting an object's relative stability with respect to a
region, combined with the use of pointer caches, look-up operations can be
made highly efficient.