  Detection of entanglement in bipartite states is a fundamental task in
quantum information. The first method to verify entanglement in mixed states
was the partial-transpose criterion. Subsequently, numerous quantifiers for
bipartite entanglement were introduced, among them concurrence and negativity.
Surprisingly, these quantities are often treated as distinct or independent of
each other. The aim of this contribution is to highlight the close relations
between these concepts, to show the connections between seemingly independent
results, and to present various estimates for the mixed-state concurrence
within the same framework.
