  We present a new paradigm for capturing the complementarity of two
observables. It is based on the entanglement created by the interaction between
the system observed and the two measurement devices used to measure the
observables sequentially. Our main result is a lower bound on this entanglement
and resembles well-known entropic uncertainty relations. Besides its
fundamental interest, this result directly bounds the effectiveness of
sequential bipartite operations---corresponding to the measurement
interactions---for entanglement generation. We further discuss the intimate
connection of our result with two primitives of information processing, namely,
decoupling and coherent teleportation.
