  Anomalous interactions involving the top quark contribute to some of the most
difficult observables to directly access experimentally. They can give however
a sizeable correction to very precisely measured observables at the loop level.
Using a model-independent effective Lagrangian approach, we present the leading
indirect constraints on dimension-six effective operators involving the top
quark from electroweak precision data. They represent the most stringent
constraints on these interactions, some of which may be directly testable in
future colliders.
