  After summarizing the characteristics of different types of dwarf galaxies I
briefly review our current state of knowledge of dwarf galaxy evolution in the
Local Group, for which we now have a fairly detailed although by no means
comprehensive picture. All Local Group dwarfs studied to date contain an old
population, though its fraction varies considerably. The majority of the dwarf
companions of the Milky Way shows evidence for a common epoch of ancient star
formation. Spatial variations in star formation are frequently observed in many
dwarf galaxies in the Local Group and beyond. These spatial variations range
from a seemingly stochastic distribution of star-forming regions in gas-rich,
high-mass dwarfs to radial gradients in low-mass dwarfs. The global mode of
star formation may be either continuous with amplitude variations or episodic.
High-mass dwarf galaxies tend to form stars over a Hubble time, whereas
low-mass dwarfs eventually cease to form stars, possibly aided by environmental
effects. Much less is known about the content and properties of dwarf galaxies
in the Local Volume, which we are trying to remedy through a large
observational effort. Dwarf galaxies in the Local Volume follow a similar trend
with absolute magnitude, mean metallicity, and central surface brightness as
the Local Group dwarfs do, and appear to be subject to morphological
segregation.
