  Unless the nearby universe is subtly anomalous, it should contain a
relatively normal selection of galaxies whose histories are representative of
field galaxies in general throughout the Universe. We can therefore take
advantage of our ability to resolve the nearby galaxies into individual stars
to directly, and accurately, measure star formation histories. The star
formation histories are determined from model-fitting analysis, based on
stellar evolution tracks, of colour-magnitude diagrams. The most accurate
information on star formation rates extending back to the earliest epoches can
be obtained from the structure of the main sequence. However, the oldest main
sequence turnoffs are very faint, and it is often necessary to use the more
evolved stars to infer the star formation history. These can then be compared
with the properties of galaxies seen over a large range of lookback times at
moderate to high redshifts. There is considerable evidence that the faint blue
galaxies seen in large numbers in cosmological redshift surveys are the
progenitors of the small late-type irregular galaxies seen in copious numbers
in the Local Group, and we concentrate on these here.
