  The problem of objectivity, i.e. how to explain on quantum grounds the
objective character of the macroscopic world, is one of the aspects of the
celebrated quantum-to-classical transition. Initiated by W. H. Zurek and
collaborators, this problem gained some attention recently with several
approaches being developed. The aim of this work is to compare three of them:
quantum Darwinism, Spectrum Broadcast Structures, and strong quantum Darwinism.
The paper is concentrated on foundations, providing a synthetic analysis of how
the three approaches realize the idea of objectivity and how they are related
to each other. As a byproduct of this analysis, a proof of a generalized
Spectrum Broadcast Structure theorem is presented. Recent quantum Darwinism
experiments are also briefly discussed.
