  Dwarf galaxies are the least massive, most abundant, and most widely
distributed type of galaxies. Hence, they are key to testing theories of galaxy
and Universe evolution. Dwarf galaxies sufficiently close to have their gas and
stellar components studied in detail are of particular interest, because their
properties and their evolution can be inferred with accuracy. This Review
summarizes what is known of the stellar and chemical properties of star-forming
dwarf galaxies closer than $\sim$20 Mpc. Given their low metallicity, high gas
content and ongoing star formation, these objects are supposed to resemble the
first galaxies that formed at the earliest epochs, and may thus represent a
window on the distant, early Universe. We describe the major results obtained
in the past decade on the star formation histories, chemical abundances, galaxy
formation and evolution of star-forming dwarfs, and the uncertainties still
affecting these results.

Astrophysics of Galaxies