We compare the characteristics of stellar populations with those of dark halos .
Dark matter around galaxies , and in groups , clusters and voids is discussed .
Modern data suggest that the overall density of matter in the Universe is \Omega _ { M } = 0.3 \pm 0.1 , about 80 % of this matter is non-baryonic dark matter , and about 20 % is baryonic , mostly in the form of hot intra-cluster and intragroup gas , the rest in stellar populations of galaxies .
All bright galaxies are surrounded by dark matter halos of external radii 200 - 300 kpc ; halos consist mostly of non-baryonic matter with some mixture of hot gas .
The Universe is dominated by dark energy ( cosmological constant ) term .
Dark matter dominates in the dynamical evolution of galaxies in groups and clusters .