The standard model of cosmology Lambda-CDM is an excellent description
of reality at large cosmological scales. However some issues remain:
(i) The measured value of the cosmological constant Lambda looks unnatural
from a quantum field perspective; (ii) The weakly interacting particles
envisaged as candidates for the cold dark matter (CDM) are still undetected
in the laboratory; (iii) The model falls short in explaining the observed
regularities in the properties of DM halos around galaxies. The prevailing
view regarding (iii) is that it should be resolved once we understand the
baryonic processes that affect galaxy formation and evolution. However,
this explanation is challenged by the fact that galactic data are in
excellent agreement with the MOND (MOdified Newtonian Dynamics) empirical
formula. In this talk we shall review the phenomenology of DM at galactic
scales and discuss some alternatives to standard CDM, including modified
gravity theories and hybrids containing some dark matter a la MOND.